Step 1 Clean the bok choy and remove any outer tough leaves. Steam until tender, 10 to 15 minutes.
Step 2 Meanwhile, combine the rice vinegar, soy sauce, sugar, ginger, green onions and 2 tablespoons of sesame oil in a small bowl and set aside.
Step 3Heat a large, heavy, nonstick skillet over medium-high heat. Add 2 tablespoons of sesame oil. Cook the tofu on both sides until golden crispy edges form, about 3 minutes a side. Be careful not to break the tofu and do not crowd the pan. Use a small spatula to turn the slices. If they start to stick in the pan, add a little more oil.
Step 4Heat a 12-inch wok or skillet over high heat. Add 2 tablespoons of sesame oil. Cook the mushrooms until tender and lightly browned, 2 to 3 minutes.
Step 5Place the tofu slices down the middle of a large rectangular platter. Arrange the bok choy along one side of the platter and place the mushrooms on the other. Pour some of the sauce over everything; pass the rest at the table.