Preheat oven to 375°F (190°C). Prepare the bell peppers by cutting off their tops, removing seeds and membranes. Lightly brush the outside of each pepper with olive oil.

Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the chopped onion and sauté for 3-4 minutes until it becomes translucent. Stir in the minced garlic and cook for an additional minute until fragrant.

Increase the heat to medium-high and add the ground turkey to the skillet. Cook for 5-7 minutes, breaking it apart with a wooden spoon, until it is no longer pink but still juicy. Season the turkey mixture with salt, pepper, Italian seasoning, and smoked paprika.

Transfer the cooked turkey mixture to a large bowl. Add the cooked quinoa or brown rice, diced tomatoes, tomato paste, and any finely chopped pepper tops (if you decided to use them). Mix all ingredients well and taste, adjusting seasoning if necessary.

Carefully spoon the prepared filling into each bell pepper, gently pressing down to ensure they are packed full but not overflowing. Arrange the stuffed peppers upright in a baking dish.

Cover the baking dish tightly with aluminum foil and bake for 30 minutes. After 30 minutes, remove the foil, sprinkle the shredded mozzarella cheese evenly over the tops of the peppers, and bake uncovered for another 10 minutes, or until the cheese is melted and bubbly.

Remove the stuffed bell peppers from the oven and let them cool for a few minutes before serving. Garnish with fresh chopped parsley or basil for a burst of freshness.