Preheat the oven to 400 °F and prep a baking tray by covering it with parchment paper or a silicone baking mat.
Finely dice the onion, bell pepper, mushrooms. Mince the garlic. Wash the cilantro, remove large stems and chop the remaining leaves (discard stems).
Cook the onion, pepper, mushrooms and garlic in a pan with the 1 tbsp oil on medium heat for 5 minutes or until the veggies have softened.
Stir in taco seasoning to coat the veggies.
Stir in the refried beans, corn and cilantro and heat through.
Cover half of one tortilla with ¼ of the mashed avocado (1/2 of an avocado) and ¼ of the prepared filling. Fold the other half of the tortilla over the top of the filling and lightly press down to seal. Repeat for the other 3 wraps.
Spray the baking tray (covered with a silicone mat or parchment paper) with oil spray. Place the quesadillas onto the tray and lightly spray the tops of the quesadillas.
Bake for 20-25 minutes, until the tortilla is crispy. Optional to flip halfway through.
Serve with salsa and sour cream.