Seed the tomato and cut into small cubes. Rinse prawns, dab dry and sprinkle with some lime juice. Clean the rocket, wash and pat dry. Wash and clean spring onion and cut half into rings. Puree avocado, buttermilk, 1/2 spring onion and rocket. Season soup with salt, pepper and a little lime juice. Put tomato cubes, spring onion rings, shrimps and corn in the middle and serve