Oh how I wish I had come up with this recipe before we attempted these at our recipe club. I combined a couple recipes I found online and came up with what we decided is a pretty good copy of the real deal. I used the pre grilled chicken that's sold at the grocery store and canned mushrooms to save time. The second time I made it I cooked the chicken and used fresh mushrooms. The taste wasn't any different and it took about 3x longer to use fresh... but the decision is yours. The amount of mushroom/water chestnuts you use can be adjusted to your preference.
2 cooked and chopped boneless/skinless chicken breasts
2/3 cup finely chopped water chestnuts
2/3 cup finely chopped and cooked mushrooms (small can)
2 chopped green onions
1 tsp minced garlic
Lettuce leaves of your choice
Garlic and red chili paste (which may seem like a waste to buy but I also use a bit of this when I make a quick homemade marinara sauce and it's delish)
For the sauce: (This is the part I made up so you may want to adjust amounts slightly depending on your tastes and how saucy you want the chicken mixture.)
About 3 T. Hoisin sauce
2 T cider vinegar
2 tsp soy sauce
1 tsp ground ginger
1/2 tsp minced garlic
Oil your skillet. Add chicken, mushrooms, water chestnuts, green onion and garlic. Stir and cook on medium-low till heated through. (If you used fresh ingredients the chicken mixture may be a little watery in which case you will want to wait until the water cooks off before adding the sauce.) While the chicken mixture is heating up, mix together the sauce ingredients in a bowl with a whisk or fork.
Once chicken mixture is nice and hot pour entire sauce mixture over it. Let it warm up again and serve in your lettuce leaves. Add a little garlic and red chili paste for an extra kick. Be forewarned a little goes a LONG way with that stuff.
I hope you like it. I know it's missing the mustard but we didn't miss it.