Heat the olive oil in a large skillet over medium-high heat. Add the bell peppers and onion and cook until softened, about 5 minutes. Add the chili powder, cumin, salt and pepper and cook for another minute.
Lay out two of the tortillas on a work surface. Sprinkle with 1/2 cup of cheese each. Top with the cooked vegetables and sprinkle with another 1/2 cup of cheese each.
Top with the remaining two tortillas. Heat a large skillet over medium heat. Place one quesadilla in the skillet and cook until golden brown on both sides, about 3 minutes per side.