Preheat oven to 375F. Cut the peppers in half, remove the seeds and stem, and place, cut side up, on a baking sheet sprayed with cooking spray.
Brush 1 TBS olive oil on top of the peppers and place them in the oven. Roast for 6-7 minutes. Meanwhile, prepare the filling.
Heat the rest of the olive oil in a large skillet, add the onions and garlic and cook until softened. Add the ground turkey and cook, breaking into small pieces with a spatula, until mostly cooked through (it's okay if some pink remains - you don't want to dry out the turkey)
Add chili powder, cumin, salt and pepper and then the crushed tomatoes. Let simmer for 6-7 minutes.
Stuff the peppers with ground turkey mixture, sprinkle cheese on top and bake for about 20 minutes, until the cheese has melted.