Toss the oil, bell peppers, onion, zucchini and lemon pepper seasoning in a medium bowl. Season the mixture with salt and pepper.
Preheat a grill pan or large saut pan over high heat. Add the vegetables and cook until they are soft and charred. Remove the pan from the heat and allow the vegetables to cool.
Place the vegetables in a bowl, add the vegan cheddar and mozzarella and scallions, and toss together.
Fill a flour tortilla with about 13 cup of the vegetable-cheese mixture, fold the tortilla in half, and set aside. Repeat with the remaining tortillas.
Heat a large, nonstick pan over medium heat and add a dab of vegan butter or a drizzle of extra-virgin olive oil. Cook the quesadillas in the pan, two at a time, about 2 minutes on each side, or until the tortillas are golden brown and the cheese has melted.
Cut each quesadilla into thirds, and top each piece with a couple of thin slices of avocado and a drizzle of the chipotle cream.
For the Chipotle Cream:
In a small bowl, mix 1 1/2 tablespoons of the thick liquid sauce in the can of chipotles with the vegan mayonnaise. Store the chiles in an airtight container and reserve for another use. Season the sauce with salt and transfer to a squeeze bottle or glass jar with a tight-fitting lid. Refrigerate for up to 2 weeks. Makes about 1 cup of cream.