In a large bowl, combine the shrimp, garlic, olive oil, lemon juice, salt and pepper. Spread the shrimp in a single layer on two 17-by-13-inch rimmed baking sheets lined with parchment paper.
Roast the shrimp, turning once, until they are opaque and firm, 6 to 8 minutes. Transfer the shrimp to a shallow dish and refrigerate, partially covered, for at least 3 hours. Serve with Green Goddess Dressing.
Green Goddess Dressing:
Process the yogurt, mayonnaise, buttermilk, if desired, parsley, chives, basil, tarragon, garlic, lemon zest, lemon juice, Worcestershire, salt, and pepper in a food processor 30 seconds or until smooth. Cover and refrigerate until ready to serve.