Brush half of the vegetable oil on one side of the pitas and set aside.
Place a medium skillet over medium-high heat.
Add the remaining 1 tablespoon of oil followed by the mushrooms, salt, and pepper. Cook, stirring frequently, until the mushrooms begin to brown, about 7 minutes.
Add the spinach and garlic, then stir until the spinach has wilted, about 2 minutes more.
Transfer the spinach mixture to a plate.
Place a baking sheet in the oven to preheat. Place the pitas, oil side down, on a clean work surface and spread with an even amount of marinara sauce, followed by the Mozzarella, the spinach mixture, Parmesan, and finally the oregano.
Carefully place the pitas on the hot baking sheet and cook until the cheese has melted and browned, about 7 minutes.
Allow to cool slightly, then cut each pizza into 4 wedges and enjoy.