Heat the oil in a large lidded pan. Cook the meatballs for 3-4 mins over a medium heat, turning often so that they brown all over. Remove from the pan with a slotted spoon and drain away any excess oil, reserving about 1 tbsp.
Add the onion and garlic to the pan and cook for 4-5 mins, stirring to soften. Stir in the soup with half a can of water. Return the meatballs to the pan and bring to the boil. Turn down the heat, cover and simmer for a further 10-15 mins until the meatballs are cooked through. Stir in the dill, mustard and some seasoning. Serve with mashed potato and cabbage.