In a small bowl, add the sauce ingredients, and whisk until well combined.
Heat the oil on medium heat in a medium size frying pan. Add the ground beef and the onions and cook until the beef is browned and the onions are translucent, about 5-7 minutes.
Stir in the water chestnuts and the sauce, and simmer on low heat until the sauce thickens, and everything is heated through, about 3-4 minutes.
Serve on butter lettuce or iceberg lettuce topped with green onions and crushed peanuts, if desired.
Notes
Storage: Store any leftovers in an airtight container, with the beef mixture and lettuce separate. The recipe will last about 3-4 days in the fridge.Substitutes: For best results, follow the recipe as is. However here are some common substitutes that would work well in this recipe.
Ground beef: You can substitute ground turkey or ground chicken
Soy Sauce: If you have a soy allergy, try tamari sauce, or liquid aminos, and you can't tell the difference in taste.
Hoisin Sauce: If you're looking for a gluten free alternative, try teriyaki sauce or just more peanut butter.
Peanut Butter: If you have a peanut allergy, you can substitute any nut butter or seed butter.