Prepare your workspace by laying the tortillas flat on a clean surface.
Mix the cheeses in a bowl, combining the cheddar and Monterey Jack.
Assemble the quesadillas by sprinkling half the cheese on one side of each tortilla, then adding black beans, red bell pepper, scallions, corn, and jalapeños. Top with the remaining cheese and fold the tortillas.
Cook the quesadillas in a heated skillet until the cheese melts and both sides are golden brown, adjusting heat as necessary.
Serve the quesadillas hot, cut into wedges, with your choice of salsa, pico de gallo, guacamole, sour cream, and a sprinkle of cilantro.