Heat wok until very hot. Add 2 T peanut oil and coat sides. Let oil heat for a few seconds. Add celery and cook about 3 minutes, stirring occasionally with wooden spoon. When just tender, transfer to platter. Add zucchini to wok and stir fry for 2 to 3 minutes. When tender, transfer to platter with celery. Add onion to wok. When half cooked, add red pepper and cook about 2 minutes, stirring occasionally. Transfer to platter with other vegetables. Next, stir fry mushrooms for 2 to 3 minutes; transfer to platter. Dredge fish in flour. Add 1 T more peanut oil to wok. Heat to very hot. Stir fry fish in 2 to 3 batches. Do not allow cubes of fish to touch each other in wok. Transfer to platter. After fish is cooked and removed from wok, add soy sauce and sherry to wok and mix. Return fish to wok and toss briefly to coat. Next add vegetables to wok and toss briefly to coat with soy mixture and to heat briefly. Serve immediately.