Combine cheddar, Monterey Jack, corn, and diced bell pepper in a bowl.
Fold each tortilla in half and lightly mark where the pumpkin face will appear.
Carefully cut small triangular eyes and a curved jack-o'-lantern mouth into the upper half of each tortilla. Alternatively, use small pieces of tomato paste or roasted pepper to form the facial features after cooking.
Open each tortilla and spread the cheese mixture evenly over one half, keeping a small border around the edge.
Fold closed and cook in a lightly buttered skillet over medium-low heat for 2–3 minutes per side, until golden and the cheese has completely melted.
Cut tiny rectangles from the green bell pepper and tuck one into the top of each quesadilla as a pumpkin stem.
Serve immediately with salsa, guacamole, or sour cream.