Wash and clean the tomatoes, dab dry and cut into slices. Peel onions and cut into rings. Wash parsley, shake dry and chop coarsely, except for a little to garnish.
Mix vinegar, salt, pepper and sugar. Fold in the oil. Arrange tomatoes and onions on plates. Pour marinade over them. Crumble sheep's cheese over the tomatoes. Sprinkle with pepper. Garnish with parsley.
It goes well with bread.