In a large mixing bowl, whisk together the mayonnaise, sweet chili sauce, lemon juice, Worcestershire sauce, horseradish, parsley, green onions, capers, salt, and black pepper until smooth.
Reserve about one-third of the dressing for serving.
Gently fold the lump crab meat into the remaining dressing until evenly coated.
Wash and dry the butter lettuce leaves, then arrange them on a serving platter.
Spoon the Crab Louie Lettuce Cups filling evenly into each lettuce leaf.
Drizzle the reserved dressing over the top or serve it on the side.
Garnish with diced cherry tomatoes and avocado.
Serve immediately while chilled.