Slice the tops off the bell peppers and remove the seeds and membranes. Lightly coat the outside of the peppers with 1 tablespoon of olive oil and place them upright in a baking dish.
In a large mixing bowl, combine the cooked quinoa, cherry tomatoes, red onion, spinach, feta cheese, olives, dried oregano, garlic powder, salt, black pepper, olive oil, and lemon zest. Mix well until all ingredients are thoroughly combined.
Stuff each bell pepper generously with the quinoa mixture, pressing down lightly to pack it in.
Once all peppers are filled, cover the baking dish with aluminum foil (to prevent sticking) and place it in the preheated oven. Bake for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 10-15 minutes, until the peppers are tender and slightly charred on top.
Remove from the oven and let cool for a few minutes before garnishing with fresh parsley.
Notes
Feel free to customize the filling with your favorite vegetables or proteins.