Add the mayo, sriracha, soy sauce, and lemon to a small mixing bowl. Whisk together and set aside in the fridge.
Salad
Peel the kani apart to create long thing strips.
Peel the cucumber. Use a sharp knife or a vegetable peeler to create ribbons of cucumber. The cucumber can also be cut into thin strips versus flat ribbons.
Peel the mango and cut it into thin strips.
Remove the shell from the avocado and cut half of it into cubes. Cut the other half into thin slices for topping
Place kani, cucumber, ¾ of the mango sliced, and the cubed avocado into a medium bowl.
Add the dressing and gently mix. Tongs work well to evenly coat the salad in the dressing.
Plate the salad and top with mango and avocado slices. Sprinkle with sesame if desired.
Notes
The salad will keep covered in the fridge for about 3 days.