In a medium bowl, mash half the black beans with a fork. Stir in the remaining whole beans, corn, bell pepper, cumin, and chili powder until well combined.
Lay out 4 tortillas on your work surface. Divide the bean mixture evenly among them, spreading it over half of each tortilla.
Sprinkle the cheese over the bean mixture, then fold each tortilla in half to create a half-moon shape.
Heat a large skillet over medium heat and add 1/2 tablespoon of oil. Place one quesadilla in the pan and cook for 2-3 minutes per side, until golden brown and the cheese is melted.
Repeat with the remaining quesadillas, adding more oil as needed. Keep the finished ones warm in a low oven while you cook the rest.
Cut each quesadilla into 3-4 wedges and serve hot with sour cream and salsa on the side. Enjoy!