Prepare all ingredients by slicing vegetables and measuring quantities.

Pat dry the beef with a paper towel and cut into bite-sized pieces. Marinate in bulgogi sauce for 10 minutes.

Heat a pan with olive oil, sauté sliced onion and bell pepper with a pinch of salt and pepper until slightly softened.

Cook the marinated beef in the pan until the liquid evaporates and the beef is browned.

Spread 1 tbsp tomato sauce on half of each tortilla. Layer pizza cheese, sautéed vegetables, cooked beef, more pizza cheese, and cheddar slices. Fold the tortilla in half.

Cook the folded quesadilla in a dry pan over low heat until the cheese melts and the tortilla turns golden brown.