In a small bowl, combine hoisin sauce, soy sauce, rice vinegar and sesame oil. Whisk well and set aside.
Heat oil in a large nonstick pan on medium-high heat. Crumble the tofu and add to the pan. Crumble the tofu further as it cooks. Sauté until it starts to turn lightly golden, about 8~10 minutes. Stir in the ginger and garlic; cook till fragrant, about 1~2 minutes.
Next add the mushrooms and cook till they start to cook down and the mixture is not wet anymore. Stir in the water chestnuts, crushed red pepper flakes and half of the chopped green onions. Cook for 1~2 minutes.
Pour the prepared sauce into the pan and stir to coat. Cook till the sauce starts to bubble and is warmed through, about 1~2 minutes. Turn off the heat and let the mixture cool slightly before serving.
To serve, spoon the mixture into individual lettuce leaves. Top with grated carrot, chopped peanuts and remaining chopped scallions. Serve right away.