Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large skillet, heat the olive oil over medium heat. Add the sliced mushrooms and sauté for about 5 minutes until they are soft.
Add the chopped spinach to the skillet and cook for an additional 2-3 minutes until wilted. Stir in the garlic powder, onion powder, cumin, salt, and pepper. Remove from heat and let cool slightly.
Place two tortillas on a clean surface. Evenly distribute half of the mushroom and spinach mixture over each tortilla. Top with mozzarella and cheddar cheese, then sprinkle with cilantro if using.
Place the remaining tortillas on top to form quesadillas.
Transfer the quesadillas to the prepared baking sheet. Bake in the preheated oven for 15-20 minutes, or until the tortillas are golden brown and the cheese is melted.
Remove from the oven and let cool for a few minutes before slicing into wedges. Serve with sour cream and salsa on the side.