Preheat oven to 375 degrees Fahrenheit.

In a bowl, combine black beans, cheddar cheese, cooked turkey or chicken, and salsa.

Season with salt and pepper to taste, if desired.

Optionally, add finely chopped onion or green onion.

Brush one side of each tortilla with melted butter.

Place one buttered tortilla, buttered-side down, on a baking sheet.

Spoon approximately 1/3 cup of the bean/turkey mixture onto one half of the tortilla.

Sprinkle with chopped onion, if using.

Fold the tortilla in half to create a quesadilla.

Repeat with the remaining tortillas and filling.

Bake for 10-15 minutes, or until the quesadillas are heated through and the cheese is melted.

Remove from the oven and let cool for 5-6 minutes.

Cut each quesadilla into thirds.

Serve with additional salsa and sour cream, if desired.