These slow cooker sandwiches are perfect for parties! Top the saucy beef meatballs with plenty of cheese and serve inside hoagie buns.
In a large bowl stir together egg, bread crumbs, 1/3 cup of the onions, the salt, oregano, and 1/4 teaspoon of the black pepper. Add ground beef; mix well. Shape meat mixture into 32 balls. Arrange meatballs in a single layer in an ungreased 15x10x1-inch baking pan. Bake, uncovered, in a 350°F oven for 25 minutes. Drain off fat.
For sauce, in a 3-1/2- or 4-quart slow cooker combine tomato sauce, the remaining 1/3 cup onions, the sweet pepper, brown sugar, mustard, chili powder, garlic salt, the remaining 1/4 teaspoon black pepper, and the hot pepper sauce. Add cooked meatballs, stirring gently to coat with sauce.
Cover and cook on low-heat setting for 3 to 4 hours or on high-heat setting for 1-1/2 to 2 hours.
Place four meatballs in each bun. Top with some of the cooking liquid and some of the cheese.