How to Make It
Fill a medium saucepan with water. Squeeze the lemon half into the water, then add it to the water with the peppercorns and a generous pinch of salt; bring to a boil. Add the shrimp and simmer until curled and just pink, about 3 minutes. Using a slotted spoon, transfer the shrimp to a paper towel-lined plate. Freeze the shrimp until just chilled, about 5 minutes.
Meanwhile, in a large bowl, whisk the lemon juice with the olive oil, grapeseed oil, sugar and a generous pinch each of salt and pepper. Add the romaine, tomatoes, avocado and shrimp and toss. Transfer to plates, garnish with the chives and serve.