Preheat the oven to 375°F.

Dice the onion and both bell peppers into small, even pieces.

Heat a large skillet over medium heat. Add the ground beef and cook, breaking it into crumbles with a spoon, until it's fully browned and no longer pink. Drain off any excess grease.

Sprinkle the taco seasoning over the beef and stir until the meat is evenly coated.

Add the diced onion, bell peppers, black beans, and drained green chilies. Cook for 2 to 3 minutes, stirring occasionally, just until the vegetables begin to soften.

Place the tortillas around the edges of a large sheet pan, letting about half of each tortilla hang over the sides while slightly overlapping the next one. Position two tortillas along each long side, one at the top, one at the bottom, and one in the center to cover the base of the pan.

Sprinkle half of the shredded Colby Jack cheese evenly over the tortilla layer, covering the bottom of the pan.

Spoon the beef mixture over the cheese and spread it into an even layer from edge to edge. Top with the remaining shredded cheese.

Place the final tortilla in the center over the filling, then fold the overhanging tortillas toward the middle, overlapping them to completely enclose the filling.

Set a second sheet pan directly on top to gently press the quesadillas flat. Transfer both pans to the oven and bake for 20 minutes.

Carefully remove the top sheet pan, then continue baking for another 15 minutes, or until the tortillas are crisp and golden brown.

Let the quesadilla cool for a few minutes before slicing into 8 large squares or 12 smaller portions.

Serve warm with sour cream, salsa, green onions, or your favorite Tex-Mex toppings.