Preheat your oven to 375°F and line a small baking dish with parchment paper.
Slice the tops off the bell peppers and remove the seeds and internal membranes to create a hollow cavity.
In a large skillet, heat the olive oil over medium heat and sauté the diced onion, celery, and minced garlic until the vegetables are softened and translucent.
Add the ground turkey to the skillet, breaking it up with a wooden spoon until it is fully browned and cooked through.
Stir in the cooked quinoa, Cajun seasoning, sea salt, and black pepper, mixing thoroughly until the filling is fragrant.
Spoon the turkey and quinoa mixture into the hollowed bell peppers, packing it down firmly to ensure they are filled to the top.
Place the stuffed peppers upright in the baking dish and roast for 25 to 30 minutes until the peppers are tender and the tops are golden brown.