Heat a large sauté pan over medium-high heat. Add olive oil. Sauté onions and garlic, stirring occasionally until fragrant (a couple of 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 the turkey is almost completely browned, add uncooked quinoa, tomato paste, 1 cup of chicken broth, chopped cilantro, and black beans. Stir well to combine, then cover. Let simmer over medium heat for 15 minutes.
While the mixture simmers, preheat the oven to 350 degrees F and slice the bell peppers in half. Remove the seeds and white membranes inside.
Place the bell pepper halves into an oven-proof dish. Fill each half with as much turkey-quinoa filling as you can. Pour the remaining ¼ cup of chicken broth into the baking dish. Cover with parchment paper and bake for 35 minutes.
Remove the pan from the oven and sprinkle each bell pepper with shredded cheese and chopped green onion tops. Bake another 10 minutes. Serve immediately.