Combine oil and five spice powder. Spread evenly onto surface of beef steak. Place steak on grid over medium, ash-covered coals. Grill, covered, 11 to 15 minutes (over medium heat on preheated gas grill, 13 to 16 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
Meanwhile, combine Sauce ingredients in medium bowl, stirring until smooth; set aside. Steam buns according to package directions; keep warm.
Carve steak into thin slices; season with salt, as desired. Spread 1 tablespoon Sauce inside each bun. Arrange beef on sauce; sprinkle with green onion, as desired. Close buns.
Nutrition information per serving: 231 Calories; 81 kcal Calories from fat; 9 g Total Fat; 2 g Saturated Fat; 3 g Monounsaturated Fat; 25 mg Cholesterol; 198 mg Sodium; 22 g Total Carbohydrate; 1 g Dietary Fiber; 16 g Protein; 2 mg Iron; 4.6 mg Niacin; 0.3 mg Vitamin B6; 0.7 mcg Vitamin B12; 2.6 mg Zinc; 15.7 mcg Selenium; 53.8 mg Choline;