Heat the oil in a large frying pan. Cook the onion and sausages over a fairly high heat for 8-10 mins, turning the sausages often so they brown all over.
Add the garlic to the pan with the kidney beans and their sauce. Half-fill one of the cans with water, swirl and then add this to the pan. Stir everything together and bring to the boil. Turn down to simmer and cook for 10 mins, or until the sausages are cooked through. Season and sprinkle with the parsley.