In a medium skillet, heat 1 tablespoon olive oil until hot. Add turkey sausage and cook until browned. Break into pieces as it cooks. Put sausage into the slow cooker.
Using the same skillet cook onion, garlic, tomato paste, oregano, and red pepper flakes. Cook until onions are softened.
Pour beef broth into the pan to deglaze pan. Make sure to scrap up any brown bits. Transfer to the slow cooker.
Add crushed tomatoes, diced tomatoes, and tomato sauce to the slow cooker. Stir ingredients together.
Place lid on top, set to low, and cook for 9-11 hours. Mine cooked perfectly at 10 hours. Add salt and pepper to, if needed, to taste.