1. Preheat the oven to 190°C. Grease a baking dish with the oil.

2. Combine the rinsed quinoa and water in a medium saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for about 15 minutes until the quinoa is cooked and the liquid is absorbed.

3. Remove the quinoa from the heat and let it sit covered for 5 minutes. Fluff the quinoa with a fork and set aside.

4. Cut the tops off the bell peppers and remove the seeds and membranes.

5. Heat the oil in a large skillet over medium heat. Add the onion and minced garlic. Sauté until softened for 2-3 minutes.

6. Add the mushrooms and cook until softened for 5 minutes.

7. Stir in the spinach leaves and cook for 2 minutes.

8. Remove the skillet from the heat. Stir in the cooked quinoa and grated Parmesan cheese. Season with salt and pepper.

9. Stuff the bell peppers with the quinoa mixture and place them in the prepared baking dish.

10. Bake for about 25-30 minutes until the peppers are tender and the filling is heated through.

11. Serve hot.