In a large, lidded frying pan, heat 1 teaspoon of the olive oil, then add the onion. Soften for 5 minutes and remove from the pan.
In a large bowl, combine the beef mince with half the cooked onion and mix well. Shape the mince mixture into approximately 20 meatballs. Using the same frying pan, heat the remaining oil and fry the meatballs in batches, until browned. Remove from the pan and set aside.
Carefully wipe the pan with kitchen towel to remove any excess liquid, then add the remaining onion along with the chopped tomatoes and spinach. Season well, cover and simmer for 5 minutes, until the spinach has defrosted. Remove the lid from the pan, then add the meatballs and cook for a further 10 minutes, until piping hot throughout and no pink colour remains in the meatballs.
Meanwhile, cook the rice following pack instructions. Serve the meatballs on a bed of rice. Garnish with parsley.