For the dressing, mix the lime juice with salt and pepper and whip in the oil. Finely chop the mint and add.
Carefully peel the avocado, remove the stone, cut the pulp into thin wedges and immediately drizzle with a little dressing. Peel the melon and cut it into thin wedges.
Layer both decoratively and drizzle with the rest of the dressing. Serve with the shrimp and lime wedges.