Pound chicken with mallet until uniform thickness, about ½ inch.
Combine ½ cup mayonnaise, soy sauce, 1 Tbsp. Sriracha, garlic, juice of ½ lime and ginger. Whisk until smooth.
Place chicken and marinade in a zip loc bag and refrigerate 5-6 hours.
Combine ½ cup mayonnaise, 2 Tbsp. Sriracha, seasame oil and juice of ¼ lime. Whisk until smooth and refrigerate until serving time.
Grill chicken over medium high heat until golden brown and juices no longer run pink - approximately 4 minutes per side. Cool.
Finely chop chicken and combine with finely chopped water chestnuts and Hoisin sauce.
Spoon 1.5-3 Tablespoons chicken filling into center of each lettuce leaf. The amount will depend on the size of the lettuce leaf.
Drizzle with Spicy Sauce and garnish with chopped green onions, if desired.