In a small bowl, mix together the chili powder, cumin, garlic powder, onion powder, salt, and black pepper.
Rub the spice mixture all over the flat iron steak and let it marinate for at least 30 minutes.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
Add the steak to the skillet and cook for 4-5 minutes on each side, or until it reaches your desired level of doneness.
Remove the steak from the skillet and let it rest for 5 minutes before slicing.
In the same skillet, add the remaining tablespoon of olive oil.
Add the sliced bell peppers and onion to the skillet and cook until they are tender and slightly charred, about 5-7 minutes.
Slice the steak into thin strips and add it back to the skillet with the vegetables.
Serve the steak and vegetables in warm tortillas with your choice of toppings.
