- Heat 1 Tbsp. sesame oil in hot large skillet over medium-high heat. Add onion; stir-fry 1 minute.
- Reduce heat to medium heat. Add remaining 1 Tbsp. sesame oil and mushrooms; stir-fry 2 minutes longer.
- Add black pepper sauce and 2 Tbsp. water; cook and stir until vegetables are evenly coated with sauce.
- Transfer immediately to serving dish. Sprinkle with green onion.