Heat 1 tbsp of the olive oil in a large saucepan over medium heat then sauté the onion and peppers for about 10 minutes.
Stir in the mushrooms, spinach, beans, spices and herbs and cook for another 4 minutes, then remove from the heat.
Thinly coat a large frying pan with some of the remaining olive oil then place over medium heat. Place a tortilla in the pan then sprinkle with a little cheese, filling, avocado, and scallion.
Fold over the the other side of the tortilla to enclose the filling; press down and fry for about 3-4 minutes until under side of the tortilla is crispy and golden.
Flip over and continue to fry for another 3-4 minutes then remove from the pan. Keep finished quesadillas warm by placing them on a baking sheet in a cool oven.
Repeat steps 3-5 with remaining tortillas and fillings then serve with plant-based "sour cream".