In a bowl, mix together olive oil, lime juice, cumin, chili powder, garlic powder, salt, and black pepper.

Add the sliced flank steak to the marinade, ensuring all pieces are well coated. Let it marinate for at least 15 minutes.

Heat a skillet over medium-high heat. Add the marinated beef and cook for about 5-7 minutes until browned.

Add the sliced bell pepper and onion to the skillet and cook for an additional 5 minutes until the vegetables are tender.

Warm the flour tortillas in a separate skillet or microwave. Serve the beef and vegetable mixture in the tortillas with your choice of toppings.