Add the meatballs, mushrooms, onion, garlic, mustard, Worcestershire, soy, thyme, paprika, onion powder, salt, pepper, and broth to the slow cooker. Cook on HIGH for 3 hours or LOW for 6 hours.
30 ounces frozen meatballs*, 8 ounces sliced white or baby bella mushrooms, 1 large yellow onion, sliced thinly, 7-8 cloves garlic, minced, 2 Tablespoons dijon mustard, 1 Tablespoon EACH Worcestershire sauce & soy sauce, 2 teaspoons dried thyme, 1 teaspoon EACH smoked paprika & onion powder, 1/2 teaspoons Morton kosher salt & freshly ground black pepper, 2 cups beef broth or stock