01 -
Lightly grease the slow cooker insert with nonstick spray or a small amount of oil to prevent sticking.
02 -
Distribute the frozen meatballs evenly in the base of the slow cooker. Scatter the thinly sliced onions over the meatballs.
03 -
Pour both cans of condensed French onion soup over the meatballs and onions. Use a spoon to gently mix until the onions are mostly coated and evenly distributed.
04 -
Cover with the lid and cook on low for 4 hours or on high for 2 hours, until the onions are softened and the meatballs are fully heated through.
05 -
Twenty minutes before serving, sprinkle the shredded Gruyere cheese evenly over the meatballs. Cover and continue cooking until cheese is completely melted and bubbly.
06 -
Spoon meatballs, onions, and plenty of sauce over mashed potatoes, toasted French bread, or steamed rice. Serve immediately for best flavor and texture.