Cook the meatballs in a non-stick pan for 6-8 minutes, then add the onion and fry a further 2-3 minutes.
Add the tomatoes, cumin and Knorr stock with 100ml water and cook for 4-5 minutes. Season with black pepper. Meanwhile cook some rice according to pack directions.
Serve the meatballs on a bed of rice, and garnish with the feta cheese.