Preheat your oven to 375°F and lightly grease a baking dish.
Slice the bell peppers in half lengthwise, removing the seeds and internal membranes.
In a large skillet over medium heat, add the olive oil and sauté the finely diced onion and minced garlic until they are soft and fragrant.
Add the ground turkey to the skillet, breaking it into small crumbles with a wooden spoon, and cook until it is completely browned.
Stir the cooked quinoa, tomato sauce, dried oregano, sea salt, and black pepper into the turkey mixture until thoroughly combined.
Arrange the bell pepper halves in the prepared baking dish and fill each one generously with the turkey and quinoa mixture.
Pour two tablespoons of water into the bottom of the baking dish, cover tightly with foil, and bake for 25 minutes.
Remove the foil, sprinkle each pepper with the parmesan cheese, and bake for another 5 to 10 minutes until the peppers are tender and the cheese is golden.