Season the shrimp all over with 1 teaspoon salt and 1/2 teaspoon pepper. Heat 1 tablespoon of the olive oil in a large skillet over high heat. Saute the shrimp in two batches, until lightly browned, about 3 to 4 minutes. With a slotted spoon, transfer to a plastic or glass container. Add the remaining oil and the remaining ingredients except the garnishes to the skillet. Season to taste with salt and pepper. Bring to a boil, reduce to a simmer, and cook until the onions are tender, about 5 minutes. Pour the vinegar mixture over the shrimp. Cover and chill overnight. Serve on baby lettuce leaves, and garnish with the radishes and green olives.