Add olive oil. Sauté onions, stirring occasionally until fragrant (a couple minutes).
Add ground turkey, cumin, garlic powder, salt, and pepper.
Break up the turkey using a wooden spoon/spatula, allowing it to brown (4-5 minutes). Once turkey is almost completely browned, add cooked quinoa and tomato sauce. Stir well to combine then cover.
Let simmer over medium heat for 5-8 minutes. While the mixture simmers, preheat the oven to 400 degrees F and slice the bell peppers in half. Remove the seeds and white membranes inside. Put bell peppers halves into an oven proof dish.
Fill each half with as much turkey-rice filling as you can. Pour ¼ cup of chicken broth into the baking dish and cover tightly with foil. Bake for 20 minutes.
Remove the foil, sprinkle each bell pepper with shredded cheese and bake another 10 minutes.