
Prepare the steak by cutting it into small strips or cubes. Set aside.
Add the oil in a large skillet over medium-high heat. Add onions in a single layer, move around to spread the oil and then let sit for a minute. Transfer the onions to a plate and set aside.
Note: Searing the onions first gives a lovely balanced of sweetness and smokiness to the onions.
To the same skillet, add the bistec strips and season with the salt, pepper and ancho chile. Cook for about 3-4 minutes stirring once in a while to cook evenly.
When the steak is half way cooked, add the garlic and mix to incorporate into the steak.
Add the onions back in, mix and cook for another 5 minutes or until the steak is nice and tender.
Serve immediately while warm.