Add all the ingredients for the sauce in a bowl, mix together, and set aside.
Heat a large pan over high heat and add in 1 tablespoon of oil. Cook the ground chicken for about 4 - 5 minutes until it's almost cooked through. Break up the chicken into smaller pieces.
Add the onions, mushrooms, white part of the scallions, and jalapenos into the pan. Stir fry together for about 1 - 2 minutes.
Add in the water chestnuts and the sauce. Stir fry for 4 - 5 minutes. Add in the green parts of the scallion and turn off the heat. Garnish with sesame seeds and cilantro for garnish. Serve inside lettuce cups.
Store leftovers in the fridge in an airtight container for up to 3 days.