Peel onions and cut them into fine rings. Cut the sausage into slices. Cut gherkins into thin slices. Cut cheese into sticks. Mix mustard, vinegar, salt, pepper and sugar. Whip oil into it. Mix sausage, onions, gherkins and cheese.
Pour vinaigrette over it. Wash parsley, dab dry and chop finely, except for a few leaves for garnishing. Wash lettuce leaves, drain and divide into 4 plates. Arrange sausage salad on top. Serve sprinkled with parsley and coloured pepper. Serve garnished with remaining parsley