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 or grill over medium-high heat. Cook the marinated beef for about 5-7 minutes until browned and cooked through. Remove and set aside.

In the same skillet, add the sliced bell pepper and onion. Sauté for about 5 minutes until softened.

Warm the flour tortillas in a dry skillet or microwave. Fill each tortilla with beef, sautéed vegetables, and desired toppings such as sour cream, cheese, guacamole, and salsa.