In a large bowl, mix ground turkey, bread crumbs, egg, chili powder, sea salt, and black pepper until uniform. Form mixture into meatballs about 2 inches in diameter.

Place meatballs in crock of slow cooker. Add garlic cloves, mushrooms, and spinach then pour marinara sauce and water over top.

Cover slow cooker and cook on low for about 6 hours or on high for about 3 hours or until meatballs are cooked through and tender. Stir before serving in order to incorporate veggies throughout sauce.