Chop the shrimp in a food processor. Add the remaining mousse ingredients and process until the shrimp are finely diced. Remove the shrimp mousse to a bowl and mix rapidly to incorporate air into the mixture.

Cut the block of tofu in half horizontally; cut each piece in half lengthwise, then crosswise, to make 8 equal pieces. Lay the tofu pieces side by side in a 9-inch glass pie pan or other heat-proof dish. Evenly spread shrimp mousse over each piece.

Place a steaming rack in a wok or saucepan. Add water to just below the level of the rack and bring to a boil. Place the dish on the rack; cover and steam until the shrimp mousse turns pink, about 6 to 10 minutes. Remove the dish from the wok and carefully pour off the cooking juices. Drizzle soy sauce and sesame oil over the tofu, sprinkle with green onions and serve.