In a bowl, combine the sliced flank steak with soy sauce, oyster sauce, hoisin sauce, sesame oil, and cornstarch. Mix well and set aside to marinate for 15-20 minutes.

Heat 1 tbsp vegetable oil in a large skillet or wok over medium-high heat. Add the bell peppers and onions, and stir-fry for 3-4 minutes until slightly softened. Remove from the pan and set aside.

In the same skillet, add the remaining 1 tbsp vegetable oil. Sear the marinated steak in batches, cooking each side for 2-3 minutes until browned. Remove and set aside.

Add garlic and ginger to the skillet and sauté for 1 minute. Return the cooked vegetables and steak to the skillet. Stir in water, rice vinegar, and honey. Simmer for 2-3 minutes until the sauce thickens slightly.

Remove from heat. Garnish with green onions and sesame seeds. Serve hot over steamed rice or noodles.