Slice the flank steak into thin strips against the grain.
In a bowl, combine olive oil, lime juice, chili powder, cumin, salt, and pepper.
Add the steak to the marinade and let it marinate for at least 30 minutes.
Slice the bell pepper and onion into thin strips.
Heat a skillet over medium-high heat and add the marinated steak.
Sear the steak for about 3-4 minutes until browned.
Add the sliced vegetables to the skillet and cook until tender.
Meanwhile, warm the tortillas in a separate pan or microwave.
Serve the steak and veggies on tortillas with desired toppings.