Separate each lettuce leaf to rinse and set it aside to dry.
Make the sauce. Combine all the ingredients in a mixing bowl. Stir or whisk until all ingredients are incorporated. You may still see bits of cornstarch, and that's ok. Set the sauce aside.
Dice onions, water chestnuts, and mushrooms. Chop up the garlic and basil.
In a medium-size cooking pan, heat your choice of cooking oil over medium-high heat.
Add garlic and onions and saute till it's slightly translucent. About 2 minutes.
Add the ground pork. Break apart the ground pork with a wooden cooking spoon to separate the meat into small clumps. Stir and cook for about 5 minutes.
Add sauce to the pan. Stir and mix until the ground pork is covered with sauce.
Add and mix water chestnuts, mushrooms, and basil with the pork and sauce. Let it simmer for about 5 minutes or until the sauce thickens.
Transfer pork filling onto a serving plate or bowl and let it cool for 5-10 minutes before serving. Serve with lettuce leaves or other fixings of your choice.