In a large frying pan cook the ground beef over medium heat, stirring to break into small chunks. Cook until no longer pink, about 5-7 minutes.
Add in diced onion and sauté for another 2-3 minutes until onions are soft, then stir in garlic and onion powder, salt, and pepper.
Transfer ground beef mixture to slow cooker and add tomato sauce, ketchup, white vinegar, brown sugar, and worcestershire sauce.
Cook on low for 5 hours or high for 3 hours. Stir the mixture and serve beef spooned onto hamburger buns with a slice of cheddar cheese.
Notes
You can make these sloppy joes ahead by cooking and freezing (once cooled) in an airtight container for up to 3 months. Thaw completely and heat before serving.