Make sauce below. Set Aside.
Add oil to large frying pan.
Add chopped onion. Cook until softened, about 3 minutes.
Add minced garlic. Stir in. Cool about one minute.
Add in ground chicken, breaking up with wooden spoon.
Once cooked, add in carrots, 1/2 of sauce. Stir continue cooking a few minutes.
Add in chopped water chestnuts.
Taste for seasoning. Add in sriacha, salt, pepper.
Arrange lettuce in platter. Add ground chicken mixture. Garnish with sliced scallion, and sesame seeds. Pour sauce over meat. Enjoy.