Slice the bell peppers in half from the stem down. Discard seeds and pith.
Sauté the onion in olive oil for 5 minutes over medium heat. Add the garlic stirring in cooking for a few more minutes.
Add the ground turkey (or protein of choice), salt, pepper, oregano, and red pepper flakes. Cook for 5 minutes until turkey is cooked through. Add vinegar, tomato paste and spinach and turn the heat off. Stir until everything is incorporated and spinach wilts.
Mix in cooked rice, olives, tomatoes, feta, parmesan, dill and mint. Taste and adjust seasonings if needed. Scoop mixture into halved bell pepper shells. Bake at 400F for 20 minutes until hot through. Allow for 10 minutes more baking time if the filling is cold.
If you prefer a softer well-cooked pepper, set on a tray, cut side up, with a tablespoon of water and bake in a preheated oven at 400F for 5-10 minutes.