1. Preheat the oven to 425°F and lightly grease a rimmed half sheet pan.

2. Heat olive oil in a large skillet over medium-high heat.

3. Add ground beef, onion, and bell pepper, then cook until the beef is browned and the vegetables are softened.

4. Drain excess grease from the skillet if needed.

5. Stir in garlic and taco seasoning, then cook for 1 minute.

6. Add tomato sauce, black beans, and corn, then simmer for 2 to 3 minutes until the filling is thick.

7. Arrange tortillas around the sheet pan so they overlap in the center and hang over the edges.

8. Place one tortilla in the center to cover any gaps.

9. Sprinkle half of the cheddar and Monterey Jack cheese over the tortillas.

10. Spread the beef filling evenly over the cheese.

11. Top with the remaining cheese.

12. Fold the overhanging tortillas over the filling and cover any open spots with another tortilla if needed.

13. Brush the top with melted butter.

14. Place a second sheet pan on top to press the quesadilla gently.

15. Bake for 18 minutes.

16. Remove the top pan and bake for another 5 to 8 minutes until golden and crisp.

17. Let rest for 5 minutes, then slice and serve with green onions, sour cream, salsa, and guacamole.