Heat 2 tablespoons peanut oil in a wok over high heat. When smoking hot add the strips of celery, carrot, red and green pepper, scallions, zucchini. Saute for approximately 2 minutes. Next add the garlic, ginger, soy sauce, chili paste, and sugar. Cook 1 minute longer. Slice the flank steak into thin pieces against the grain. Add the steak to the wok and toss until just warm. Transfer to a serving dish, and enjoy.