Preheat the oven to 450�F.
Slice the tofu lengthwise into four slices, then cut each slice diagonally into two more slices. Place the tofu slices onto a plate, and cover with plastic wrap. Top with another plate and a heavy item, and let stand 10 minutes.
Whisk the hoisin sauce, vinegar, brown sugar, light soy sauce, mustard, chili garlic sauce, and garlic in a small bowl. Spread 1/3 of the mixture in a baking dish. Drain the tofu, arrange in the baking dish, and top with the remaining hoisin mixture. Bake 10-15 minutes until heated through.
Boil 1 inch of water in a pot with a steamer basket. Steam the bok choy for 6-8 minutes or until tender, then transfer to a plate. Sprinkle with the sesame oil.
To serve, place 2 bok choy halves and 2 tofu slices on each plate.
