For Sriracha Mayo, combine all ingredients. Refrigerate at least 1 hour before using to allow flavors to blend.
For the Turkey Club, spread butter on one side of each slice of bread. Toast, butter side down, until top of bread is medium golden brown. Spread spicy honey mustard on unbuttered side of bread. Then layer with lettuce, tomato, onion, bacon, deli turkey, avocado slices and sprouts.
Spread Sriracha Mayo over unbuttered side of second slice of bread. Place sriracha side down over sprouts. (Refrigerate remaining Sriracha Mayo for up to 1 week.)