Drain and rinse the kidney beans in a colander to get rid of the dark sludge from the tins.
Put the onion slices into a bowl and pour over the vinegar. Leave to macerate for about 15 minutes.
Halve the cherry tomatoes and put them into a bowl.
When you are ready to assemble the salad, combine the drained kidney beans, macerated onions and halved tomatoes, tossing together well. Dress with the olive oil.
Recipe courtesy of Nigella Lawson(Copyright 2004, Feast, Hyperion, All Rights Reserved)