In a small bowl, mix together oyster sauce, sesame oil, sugar, and light soy sauce. Set sauce aside for later.
Fill large pot with water and bring to a boil. While waiting for water to come to a rolling boil, prepare vegetables. Clean and cut bok choy into smaller pieces. If you are using baby bok choy, cut bok choy in halves. If you are using larger bok choy, cut bok choy into quarters. Chop up garlic into small pieces.
Once water has come to a boil, add cleaned and prepped bok choy. Boil bok choy for 2 minutes. Remove bok choy, drain, and plate all the bok choy.
In a small pan, heat up 2 tablespoons of oil. Add garlic and chili oil and stir with low heat for about 1-2 minutes or until fragrant and garlic has softened. Stir constantly to prevent burning the garlic. Add in the oyster sauce, soy sauce, sugar, and sesame oil mixture. Stir fry for another 30 seconds.
Pour sauce over bok choy and serve immediately.