This is an option that addresses the context you have provided. It could also be considered as "intensely-focused..." but then the text starts to deviate into technical areas...

It is just a suggestion.

The term “unitasker” is used in two different ways. In the first sense, it refers to an object with one function, such as a rice cooker. It is also sometimes used in reference to people, as a description for someone who only completes one task at a time. Some people view unitaskers unfavorably in certain situations, whether they are objects or people, with the implication that the ability to perform multiple tasks is vital.

http://www.wisegeek.com/what-is-a-unitasker.htm

Single-minded is the correct phrase here, as it means precisely what the writer goes on to explain in Spanish that he means: that he focuses entirely on one thing (work in this case) at the expense of all else.
One-track mind means something quite different: to be obsessively preoccupied with something, usually in a negative sense.
And uni tasker or some similar quasi word is far too technical for an opinion piece.

In an opinion piece you can no doubt use some poetic licence - as in the following examples:

Filling Your Freezer and Other Frugalitarian Ideas I will admit that it has not been easy as I am a multi-tasker, think aheader and I have had to become a one thing at a timer and moment by momenter :o) ...
fillingmyfreezer.blogspot.com/ - 63k - Cached - Similar pages
jenn-a-juiceGrad School forces even the most adamant one-thing-at-a-timer to learn the art of multitasking. For example, more often than not, any kind of food is eaten ...
jennajuice.blogspot.com/2007/05/top-5-ways-grad-school-prepares-you-for.html - 76k - Cached - Similar pages
[PDF] ORAL HISTORY OF LAWRENCE BRADFORD PERKINS Interviewed by Betty J ...File Format: PDF/Adobe Acrobat - View as HTML
is basically a one-thing-at-a-timer. His mind did not enjoy keeping six things. in the air at the same time, never did. He had both great strength and great ...
www.artic.edu/aic/libraries/caohp/perkins.pdf - Similar pages

If this is the complete context, (or something very similar)

"...Los hombres se olvidaron de que la mujer funciona diferente que ellos, simplemente porque no es un hombre.

El hombre, aunque tenga varios roles en su vida, es un personaje uni-canal, que cuando está trabajando está totalmente concentrado en el trabajo y se olvida de que es esposo y padre. Cuando representa el rol de esposo, no piensa en su trabajo ni de chiste. Su cerebro está programado para pensar en una sola cosa a la vez.

La mujer, en cambio, puede estar en cinco asuntos al mismo tiempo. Puede perfectamente, estar atendiendo una llamada de negocios y cambiando un pañal, mientras revisa la tarea de otro de los niños y le entrega a la cocinera una nota con el menú del día siguiente.

No es nada del otro mundo, porque Dios dotó a las mujeres de un cerebro "multi-canal", que las hace capaces de ejercer varios roles al mismo tiempo, sin que uno u otro se vea deteriorado.

¿Cuando surgió el dilema?

Hasta antes del siglo XIX, el trabajo era una parte integral de la vida de la mujer, quien representaba sus roles de esposa, madre, ama de casa y trabajadora, de una manera natural. Nadie se escandalizaba de saber que la esposa salía de la casa para atender a algún enfermo, el puesto en el mercado, el comercio familiar, el trabajo en la agricultura o en la granja. La mujer siempre había trabajado como mujer (no como hombre) y eso era lo natural. En su casa, guardadas, sólo se quedaban las mujeres enfermas o minusválidas. ..."


Then, the word you're looking for is definitely "monotasker" is the term you're looking for.

I doubted myself, because of the way it is said in Spanish, but the complete paragraphs shed light.

In fact, women ARE known to be multitaskers, versus men, who are monotaskers. In Chile there's a joke that says men can't chew gum and walk at the same time... They give a step, stop, then chew, haha!

• Word Spy - monotasking
—monotasker n. Example Citations:. What's wrong with monotasking? ... Back in the lazy mono-tasking days, even if you were a multi-tasker, you didn't like ...
http://www.wordspy.com/words/monotasking.asp

• Cheerio Road: The myth of multitasking
I am a monotasker. By that I mean I do things one at a time. I used to think I was a multitasker. Now I'm not so sure that anyone is a multitasker, ...
http://mommazen.blogspot.com/2008/08/myth-of-multitasking.ht...

• The New York Times > Fashion & Style > Road-tripping With ...
"Johnny is a huge multitasker," he said. "I'm not. I'm a monotasker, barely." "A demitasker," Mr. Adler added. "One-track Wilma," Mr. Doonan said. ...
http://www.nytimes.com/2005/04/03/fashion/03adler.html?pagew...

• Word Spy - monotasking
Performing one task at a time (cf. multitasking). Also: mono-tasking. —monotask v., adj. —monotasker n. Example Citations:. What's wrong with monotasking? ...
http://www.wordspy.com/words/monotasking.asp

• The new efficiency booster: monotasking
File Format: PDF/Adobe Acrobat - View as HTML
any comparison to monotasking until recently. Multitasking has already been identified as a contributor to the sensation of time ...
https://www.quickbase.com/up/7rxtwe3r/g/rcy/ej/va/monotaskin...

• Real Estate Blog - The Art of Monotasking
Financial guru Suze Orman is an advocate of monotasking. "I, more than anybody I 've ever met, do not believe in multitasking," she says. ...
http://activerain.com/blogsview/501434/The-Art-of-Monotaskin...

• Cheerio Road: The myth of multitasking
I monotask what I love. The rest just gets done...eventually. ... Now, if you played the flute while folding the laundry, that would be multitasking. ...
http://mommazen.blogspot.com/2008/08/myth-of-multitasking.ht...

• Monotasking: a cure for what ails ya
I totally agree on monotasking. Multi-tasking means doing lots of things not very well. Here’s my personal mantra when I have a spare fifteen minutes and ...
http://www.myorganizedbiz.com/monotasking-a-cure-for-what-ai...

this may be applicable due to the use of 'canal' in the source text, i think we are talking more about the subjects' thought process and focus of concentration rather than the ability to do more than one task at the same time....although this is often the source of women's jokes about men...;)

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Note added at 16 hrs (2008-10-06 10:04:52 GMT)
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i do not wish to imply that this is a commonly used word in english, simply that it may be suitable for the technical nature of the commentary