Prepare the sauce by mixing the hoisin sauce, soy sauce, rice vinegar, and sesame oil in a small bowl.
Heat the grapeseed oil in a large skillet over medium-high. Then crumble in the tofu. Cook for about 5 minutes, then stir in the water chestnuts, garlic, ginger, red pepper flakes, and half of the green onions about 1 minute more.
Pour the prepared sauce over the tofu mixture and stir to coat. Cook until the sauce is warmed through, about 1 – 2 minutes.
Spoon the tofu mixture into the large lettuce leaves—top with remaining green onions and veggies of choice.