Prepare the ingredients by slicing the meat into thin strips about 2 inches long and ¼ inch wide (shrimp should be cleaned and deveined but remain whole).
Slice peppers and onions into similar 2 inch by ¼ inch strips.
Pat chicken, beef or shrimp dry with paper towels to absorb any extra moisture, and add to a mixing bowl.
To the meat (or shrimp), add the 1 teaspoon of ground cumin, 1 teaspoon of garlic powder, the juice of 1 whole lime, salt and pepper, and 1 ½ tablespoons of vegetable oil. Toss gently to coat.
Heat a large cast iron skillet to medium high heat with the other half of the vegetable oil (1 ½ tablespoons).
Once hot, add the sliced pepper and onion strips to the oil and saute for 2-3 minutes until the onions are translucent and the peppers soften.
Use tongs or a spatula to remove the peppers and onions to a plate temporarily.
To the same hot skillet, lay down the meat or shrimp in a single layer, without moving it so that it may develop a dark sear. This will take about 2-4 minutes.
Once the protein has developed a thick brown sear, add the partially cooked peppers and onions that had been set aside back to the pan.
Saute for an additional 2-3 minutes until the meat is fully browned (or shrimps are pink and tails curled).
Turn off the heat and serve sizzling hot with warm tortillas right away.
Add additional toppings as desired.