Prepare the tofu by pressing it between a heavy board on top to get rid of excess water. The longer you leave the heavy board on top, the more excess water will come out. Then slice the tofu in bite sizes, about ½ inch in size.
Wash the bok choy with cold water and slice the bok choy lengthwise.
Combine soy sauce, rice vinegar, sesame oil, sesame seeds, black pepper, cornstarch, and water, dissolve the cornstarch, and mix everything until well blended. Set it aside.
In a shallow dish, combine cornstarch, garlic powder, onion powder, salt, and black pepper. Mix well until well blended. Coat all the tofu cubes using the cornstarch mixture, making sure all the sides are coated well.
Fry the tofu in a frying pan with preheated cooking oil. Be sure the oil is hot enough, and fry the tofu in two batches, flipping the sides and cooking until golden brown.
In a wok, heat two tablespoons of cooking oil, and cook the garlic until aromatic. Toss the bok choy and stir-fry in high heat for 1-2 minutes.
Lower the heat to medium, add the sauce mixture, stir, and let it thicken for a minute. Then add the fried tofu and stir everything until it is coated with the thick sauce. Sprinkle with sesame seeds to serve. Enjoy!