Step 1 :Combine all ingredients in a food processor and process until smooth. The result will not be your typical thick pesto it will be more of a marinade. Step 2 :Pour parsley pesto into a shallow bowl and add shrimp to marinate for approximately 15-20 minutes. Step 3 :Grate your tomatoes and spoon onto a long serving dish or large serving plate and season with salt and pepper. Step 4 :Top with shrimp that has been marinating in pesto. Step 5 :Garnish with diced onion and drizzle a bit of the pesto marinade all over. Step 6 :Serve and enjoy!