01 -
Coat the insert of your slow cooker evenly with nonstick cooking spray to facilitate cleanup and prevent sticking.
02 -
Distribute frozen meatballs in an even layer along the bottom of the slow cooker. Scatter thinly sliced onions over the meatballs.
03 -
Pour both cans of condensed French onion soup over the onions and meatballs. Use a spoon to gently mix so sauce and onions coat the meatballs evenly.
04 -
Cover with the lid and cook on low for 4 hours or on high for 2 hours, until onions are very soft and meatballs are heated through.
05 -
Twenty minutes before serving, sprinkle the shredded Gruyere cheese evenly over the meatball mixture. Cover and continue cooking until the cheese is melted and bubbling.
06 -
Spoon meatballs and caramelized onions with sauce over mashed potatoes, toasted French bread, or rice. Serve immediately while hot.