Combine mayonnaise, crème fraîche, Tabasco, tomato ketchup, lemon juice and garlic in a bowl and mix well to combine, season to taste.
Add prawns and chives, toss to lightly coat.
Place bottom half of buns out on a work surface, cut side up.
Top with avocado, lettuce, sandwich and prawn mixture.
Sandwich with the top halves and serve.