**Prepare the Filling:** Heat olive oil in a skillet over medium heat. Add the diced onion and bell pepper, cooking until softened, about 5 minutes.
**Cook the Meat:** Add the ground meat to the skillet, breaking it apart with a spatula. Cook until browned, then drain excess grease.
**Season the Filling:** Stir in taco seasoning and water. Simmer for 2-3 minutes. Add black beans and mix until combined. Remove from heat.
**Preheat the Oven:** Preheat your oven to 425°F (220°C).
**Assemble the Quesadilla Base:** Spray or lightly grease your sheet pan. Lay 4 tortillas over the bottom of the pan, letting them hang over the edges to cover the sides. Place one tortilla in the center to cover the exposed pan.
**Add the Filling:** Spread the meat and vegetable mixture evenly over the tortillas. Sprinkle the shredded cheeses on top.
**Top and Seal:** Place another tortilla in the center, then fold the overhanging tortillas toward the center to seal the quesadilla. Spray or brush the top with cooking spray or melted butter.
**Bake:** Place a second sheet pan on top of the quesadilla and press lightly to flatten. Bake for 20 minutes, then remove the top pan and bake for an additional 5 minutes to crisp up the top.
**Slice and Serve:** Allow the quesadilla to cool for 5 minutes before slicing into squares or wedges. Serve with your favorite toppings.