Step 2: Heat a skillet over medium heat; cook and stir beef until browned, 5 to 7 minutes. Add onions and green bell peppers to beef; cook and stir until softened, 5 to 10 minutes. Pour barbeque sauce over beef mixture and simmer until sauce is slightly reduced, about 10 minutes.

Step 3: Lay 4 tortillas on a baking sheet and top each with beef mixture and Cheddar cheese. Top each Cheddar cheese layer with a tortilla.

Step 4: Bake in the preheated oven for 10 minutes; flip the quesadillas and cook until cheese is melted, about 5 minutes more.