Preheat oven to 425 degrees. Line a baking sheet with parchment paper and set aside.
Spray large nonstick skillet with cooking spray and heat over medium heat.
Add leeks and mushrooms and cook until tender, about 5 minutes. Add garlic and cook until golden, about 1 to 2 minutes (watch carefully to not over cook garlic). Season with salt and pepper.
Place pitas on prepared baking sheet. Spreach each pita with 2 tablespoons ricotta cheese. Drizzle with 1 teaspoon olive oil, and top with vegetable mixture. Sprinkle with Parmesan cheese and red pepper flakes (if using).
Bake until pita is golden and cheeses begin to melt, about 6 to 8 minutes. Serve immediately.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2012/04/04/mushroom-and-leek-pita-pizzas/