Heat olive oil in a large nonstick skillet over medium heat. Brown the turkey, crumbling with a wooden spoon.
Add the diced onion and sauté for 5 more minutes, or until the turkey is cooked through and onion is soft. Season with the oregano, fennel seeds, chili flakes and ½ tsp. kosher salt, or to taste.
Transfer the turkey and onions to a 5 to 6 quart slow cooker, followed by the bell peppers, rice, tomato sauce, chicken broth, and garlic powder. Stir in an additional ½-1 tsp. kosher salt, or to taste. Mix well to combine. Cover and cook on HIGH for 3 ½ to 4 hours, or until rice is tender.
Remove the lid and stir a few times. Fold in 1 cup of the cheese, then season to taste with additional salt.
Divide among 4 meal prep containers and top each with 1 tbsp. of the remaining cheese. Allow to cool, then cover and refrigerate for up to 4 days.