Heat up the oil over medium high heat in a large skillet, then brown the pork for 3 minutes, stirring enough so it doesn’t burn. Add the water chestnuts and tofu.
Mix up the scallions, ginger, garlic, hoisin, soy sauce, and sriracha. Add to the pan, and toss all the ingredients. Cook for a few more minutes until the pork is cooked through. Remove from the heat and add the sesame oil.
At the table, fill each lettuce cup with rice and a big spoonful of the pork mixture.