In a skillet, reheat the leftover taco meat over medium heat. If the meat seems dry, add a tablespoon of water or broth and stir until warmed through.

Optionally, sauté the chopped onion and bell pepper until softened and fragrant, then mix them into the taco meat.

Lay one tortilla flat on a clean surface. Spread about ½ cup of the taco meat evenly over half of the tortilla.

Sprinkle ⅓ cup of shredded cheese over the meat. Fold the tortilla in half to form a semicircle. Repeat for the remaining tortillas.

Heat 1 tablespoon of butter or oil in a large non-stick skillet over medium heat.

Place the folded quesadilla in the skillet and cook for 2-3 minutes on one side, or until golden and crispy. Flip carefully and cook the other side for another 2-3 minutes. Repeat with remaining quesadillas, adding more butter or oil as needed.

Remove the quesadillas from the skillet and let them cool slightly before cutting into wedges.

Serve with your favorite toppings, such as salsa, guacamole, or sour cream, for dipping.