Make the special sauce by dissolving the sugar in water in a small bowl. Add soy sauce, rice wine vinegar, ketchup, lemon juice and sesame oil. Mix well and refrigerate sauce until ready to serve.
Combine the hot water with the hot mustard and set aside. Eventually add your desired measurement of mustard and garlic chili sauce to the special sauce mixture to pour over the wraps.
Bring oil to high heat in a wok or large frying pan. Saute chicken breasts for 4 to 5 minutes per side or until done. Remove chicken from the pan and cool.
Prepare the stir fry sauce by mixing the soy sauce, brown sugar, and rice vinegar together in a small bowl. Add red pepper flakes, if desired.
With the pan still on high heat, add another tablespoon of vegetable oil. Add chicken, garlic, onions, water chestnuts and mushrooms to pan. Add stir fry sauce to pan, saute mixture a couple minutes then serve in lettuce leaves.