Trim the base of the bok choy, split vertically and rinse well fanning the leaves to remove any sand or dirt. Drain off excess water and slice diagonally.
Slice mushrooms and celery thinly.
Peel and seed cucumber. Cut vertically into quarters and then cut into 3" lengths.
Mince the garlic.
Combine the broth, soy sauce, cornstarch in a small dish and mix well.
Heat the vegetable oil in a wok or large skillet.
Add the garlic and let if fry about 30 seconds.
Add the bok choy and mushrooms and stir fry about 2 minutes.
Add the celery and cucumber and stir fry another 3 minutes.
Add the broth mixture and stir fry another 4 minutes or so until vegetables are tender crisp.
Stir in sesame oil 30 seconds before transferring mixture to a serving bowl.