Preheat your oven to 375°F (190°C).
Slice the bell peppers in half lengthwise and remove the seeds and membranes.
In a large skillet, heat the olive oil over medium heat and sauté the diced onion and minced garlic until they become translucent and fragrant.
Add the ground turkey to the skillet, breaking it apart with a spatula, and cook until it is completely browned and no longer pink.
Stir in the cooked quinoa, tomato puree, dried oregano, sea salt, and black pepper, allowing the mixture to simmer for 3 minutes to meld the flavors.
Arrange the pepper halves in a baking dish and spoon the turkey and quinoa filling generously into each cavity.
Cover the dish with foil and bake for 25 minutes, then remove the foil and bake for an additional 5 minutes until the peppers are tender.