Preheat oven to 400 degrees F.
Lay 1 tortilla on a clean work surface. Spread the beans evenly over the tortilla. Spoon 3/4 cup of salsa over the beans, then sprinkle with the cheese. Top with the second tortilla. Place the quesadilla on a foil-covered cookie sheet.
Bake for approximately 15 minutes, or until the cheese is melted and the top is crisp and brown. Meanwhile, swirl the guacamole and sour cream together in a small bowl. Cut the quesadilla into 4 equal portions and transfer to a plate. Serve with the guacamole mixture and remaining 1/4 cup of salsa.