Heat a 12-inch skillet over medium heat.
Spray a tortilla with non-stick cooking spray. Place it flat on heated skillet for 1 minute and flip tortilla over.
Sprinkle 1 cup cheese on the tortilla, followed by ½ cup each corn and beans and 4 slices avocado.
Place another tortilla on top to make a sandwich. Cover pan with lid.
After 1 minute, flip the quesadilla.
When the cheese has melted, remove quesadilla and place on a warm plate; repeat with remaining tortillas, vegetables and cheese.
Cut each quesadilla into 4 wedges. Top each piece with a dollop of salsa and sour cream before serving.