Rinse the Sichuan cabbage very well and pat dry with paper towels. Chop into very small minced pieces.

Cut off and discard the stems from the mushrooms. Wash the mushrooms with cold water. Pat dry with paper towels and mince very fine. In a small bowl, mix the mushrooms with the Sichuan cabbage. Sprinkle with the cornstarch and sugar and set aside.

Rinse the bok choy with cold water and pat dry with paper towels. Cut each baby bok choy crosswise 4 times. Cut the tofu into 12 squares, about 1½ inches square by ¾ inch thick. Set the tofu squares on a cloth to drain the excess water out. Scoop some tofu out of the center of each square, reserving the scooped-out tofu. With a fork, mash about half of the scooped-out tofu and add to the mushroom mixture (it should be the consistency of paste). Put about 1 teaspoon of the mixture in each square of tofu, being very careful not to tear the tofu. Pat the filling down carefully. Repeat until all 12 pieces are filled and set aside.

Heat a large nonstick pan or wok over high heat. Add 1 tablespoon vegetable oil and stir-fry the baby bok choy for 1 minute. Add ½ teaspoon ginger, ½ teaspoon garlic, and the salt, and stir well. Add 2 tablespoons water and cook until the vegetables change color, about 2 minutes. Remove the bok choy to a platter.

Wash the pan and reheat with the remaining 1 tablespoon vegetable oil, ½ teaspoon ginger, and ½ teaspoon garlic. Carefully place the stuffed tofu squares, one at a time, in the pan and panfry both sides until slightly brown, about 2 minutes. Add more oil if needed.

Add the oyster sauce and coat the squares. Cook until the sauce is absorbed into the tofu, about 2 minutes. Turn off the heat and place the tofu on top of the baby bok choy, Serve immediately.