Upgrade your appetizer game with these easy slow cooker Meatball Sliders. Keep the meatballs simmering all day and allow guests to build their own if the bash is an open house or all day affair.
Place onion wedges in a 3 1/2- or 4-quart slow cooker. Top with frozen meatballs. In a medium bowl combine marinara sauce, balsamic vinegar, and crushed red pepper. Pour over meatballs.
Cover and cook on low-heat setting for 4 to 5 hours or on high-heat setting for 2 to 2 1/2 hours.
Gently stir through mixture in cooker. Place a cheese and a tomato slice on the bottom of each cocktail bun. Top each with a meatball;replace bun tops.