Lay the tortillas flat on a clean work surface.

In a medium bowl, place the cheddar and Jack cheeses and toss to combine.

Sprinkle half the cheese evenly over one half of each tortilla, leaving the other half bare. Evenly sprinkle the black beans, red peppers, scallions, corn, and jalapeños over the cheese. Top with the remaining cheese, then fold the bare half of each tortilla over the fillings to create a half-moon shape.

Heat a dry cast iron skillet over medium-low heat. When hot, add two of the quesadillas and cook until the cheese is melted and the quesadillas are browned on both sides, 1 to 2 minutes per side. If the tortillas are browning faster than the cheese is melting, reduce the heat. Repeat with the remaining quesadillas.

Slice and serve with salsa, pico de gallo, guacamole, sour cream, and/or cilantro, as desired.