In a large nonstick pan, cook peppers, onion, and mushrooms in olive oil over medium to medium-high heat for about 7 minutes, or until just tender. Add in tomato and cook for 1 additional minute.
Remove vegetables from pan.
Coat the same pan with cooking spray, and place one tortilla in pan.
Place 1 GO VEGGIE Lactose & Soy Free Pepper Jack Deli Slice over tortilla, and layer 3/4 cup of the vegetable mixture over the cheese. Top with a second tortilla.
Cook until golden on both sides, for approximately 2 to 3 minutes per side. Remove quesadilla from pan, and repeat with remaining ingredients. Cut each quesadilla into 8 triangles with a pizza cutter. Serve hot.