Step 1: Marinate the Beef

1. Slice the flank steak thinly against the grain for tender bites.
2. In a bowl, whisk together the egg, cornstarch, salt, and cold water.
3. Add the beef slices to the marinade, ensuring every piece is coated. Let it rest for 15–20 minutes.

Step 2: Prepare the Sauce

1. In a small bowl, mix water, honey, ketchup, hoisin sauce, soy sauce, oyster sauce, sweet chili sauce, rice wine vinegar, red pepper flakes, and cornstarch.
2. Stir until the cornstarch dissolves completely, then set the sauce aside.

Step 3: Fry the Beef

1. Heat the vegetable oil in a skillet or wok over medium-high heat.
2. Coat each piece of beef lightly in cornstarch before frying.
3. Fry the beef in small batches to ensure crispiness, about 2–3 minutes per batch. Place fried beef on a paper towel-lined plate to drain excess oil.

Step 4: Sauté the Vegetables

1. Remove excess oil from the skillet, leaving about 1 tablespoon.
2. Add the red bell pepper, yellow onion, and garlic.
3. Sauté for 3–4 minutes until the vegetables are slightly softened but still crisp.

Step 5: Combine with the Sauce

1. Pour the prepared sauce into the skillet and bring it to a simmer over medium heat.
2. Stir continuously until the sauce thickens, about 2–3 minutes.
3. Return the fried beef to the skillet, along with the sautéed vegetables.
4. Toss everything together to ensure the sauce coats the beef and veggies evenly.

Step 6: Serve and Enjoy

1. Serve hot over steamed rice or noodles.
2. Garnish with sesame seeds or sliced green onions for extra flavor.