In a skillet, over med-high heat, cook the ground beef; adding the salt & pepper, until completely cooked. Drain off any grease and place beef in a medium size bowl. Add the 2 cheeses and onions into the bowl with the hamburger meat and thoroughly mix; creating a "cheeseburger mix".
Place an equal amount of the cheeseburger mixture on each tortilla; by placing the mixture only on half of each side of the tortilla. Fold each tortilla over to create a "half moon" shape and press down lightly.
Lightly coat a skillet with the cooking spray and heat over med-high heat. Lightly brown each quesadilla for 2-3 minutes on each side until the cheese melts. Remove quesadillas from pan, place on a clean work surface and cut each quesadilla into 3 wedges. Serve hot, with your favorite cheeseburger SIDE fixings like shredded lettuce, tomatoes, pickles, ketchup & mustard.