Heat olive oil in a skillet over medium-high heat. Add sliced flank steak, cumin, chili powder, salt, and black pepper. Cook until steak is browned and cooked through, about 5-7 minutes.

In the same skillet, add sliced bell pepper and onion. Sauté until softened, about 3-4 minutes.

On one half of each tortilla, layer cooked steak, sautéed vegetables, and shredded cheese. Fold the tortilla over to create a half-moon shape.

Wipe the skillet clean and return to medium heat. Cook each quesadilla for 3-4 minutes on each side, or until golden brown and cheese is melted.

Cut quesadillas into wedges and serve warm with salsa or sour cream.