For the filling, heat the oil in a pan on medium heat. Add onion, ginger, lemongrass, and garlic and sauté for 7-10 minutes, or until onions soften. Add the tofu and water chestnuts, crumble the tofu into small pieces.
Fry for about 4 minutes. Then add the soy sauce, the hoisin sauce and the chilli sauce. Transfer the filling to a bowl for serving.
Place the lettuce leaves on a serving plate and place the side dishes in small bowls. The guests can now take a leaf of lettuce each, fill the tofu mixture in the middle and place the side dishes on top.
Then roll up the lettuce leaf into a wrap and enjoy. It can be eaten with the fingers.