In a bowl, mix olive oil, cumin, chili powder, garlic powder, and salt. Add flank steak and marinate for at least 30 minutes.

Heat olive oil in a skillet over medium heat. Add onions and bell peppers; cook until softened and slightly charred (5–7 minutes).

In the same skillet, cook marinated flank steak over medium-high heat for about 4–5 minutes on each side until desired doneness. Let rest before slicing thinly against the grain.

Place shredded cheese on one half of each tortilla. Top with sautéed veggies and sliced steak; fold to create a half-moon shape.

Wipe excess oil from the skillet. Cook each quesadilla over medium heat until golden brown (3–4 minutes per side).

Let cool slightly before slicing into wedges. Enjoy with salsa, guacamole, or sour cream.