Kids love them because they're a vehicle for cheese, parents love them because they also contain nutritious vegetables.
In a medium-size bowl, mix together the carrot, broccoli, onion (if desired), and cheese.
Set a large nonstick frying pan over medium heat and thinly coat the bottom of the pan with canola oil. Place a tortilla in the pan, cover it with the cheese-veggie mixture, and drizzle the salsa or taco sauce on top.
When the bottom of the tortilla is lightly browned and the cheese has melted, fold the quesadilla in half and transfer it to a plate. Cut it into quarters and serve hot. Makes 1 quesadilla.