Combine the salt, garlic powder, oregano, cumin and black pepper in a small bowl. Season the steaks on both sides with the seasoning mix.

Heat 2 tbsp. of oil in a large (very large) skillet over medium-high heat. When the oil is very hot, almost smoking, add as many steaks that will fit in the skillet without overcrowding.

Cook the steaks about 2-3 minutes per side, until they’re golden brown and cooked through. Take the skillet off the heat, remove the steaks to a plate or pan and keep warm. Repeat with the remaining steaks. Note: It may be necessary to add another tablespoon of oil to cook the second batch of steaks.

Do not wash the skillet, return it to medium-low heat and add the sliced onions. Cook the onions, stirring frequently, for 3-5 minutes until they start to soften, stirring frequently. Remove the skillet from the heat and set aside.

Cut the loaves of bread to make 4 large pieces. Then open each piece by slicing it in half lengthwise.

Add one steak and a quarter of the onions to the bottom half of the bread piece. Then add the mayonnaise, lettuce and tomato slices, if using. Add a generous amount of potato sticks and cover with the top piece.

Gently, press the pan con bistec for a few minutes until the bread is toasty and starting to flatten out. If desired, brush a little bit of butter on the bread top prior to pressing to get a pretty sheen.