Preheat the air fryer: Set it to 375°F (190°C).
If your model needs preheating, give it 3–5 minutes.
Cook the veggies: Heat a skillet over medium with 1 tablespoon oil. Sauté onion and bell pepper for 3–4 minutes until slightly softened. Add mushrooms, zucchini, garlic, and seasonings.
Cook 3–4 more minutes until tender and most moisture evaporates. Stir in spinach at the end to wilt. Taste and adjust salt and pepper.
Prep the tortillas: Lay out tortillas.
Sprinkle a thin, even layer of cheese on half of each tortilla. Add a layer of the cooked veggie mixture (about 1/3–1/2 cup per quesadilla). Add any optional beans or chiles.
Top with a little more cheese to help seal, then fold the tortilla in half.
Lightly oil: Spray or brush the outsides of the folded tortillas with a bit of oil. This helps them brown and crisp.
Air fry: Place quesadillas in a single layer in the basket. Don’t overcrowd; work in batches if needed.
Cook for 3–4 minutes, flip carefully, then cook another 3–4 minutes until golden and the cheese is melted.
Rest and slice: Let them sit 1–2 minutes to set. Slice into wedges. Sprinkle with cilantro and a squeeze of lime if you like.
Serve: Pair with salsa, guacamole, and a dollop of sour cream or Greek yogurt.