Prepare the sauce: In a bowl, mix soy sauce, hoisin sauce, brown sugar, honey, rice vinegar, sesame oil, minced garlic, grated ginger, and optional chili flakes. Stir well to combine.

Sear the beef: In a large skillet or wok, heat a little sesame oil over medium-high heat. Add the thinly sliced beef in a single layer, cooking for 2-3 minutes on each side until browned.

Cook the sauce: In the same skillet, pour in the prepared sauce mixture and bring it to a gentle simmer.

Thicken the glaze: Once the sauce starts to simmer, add the cornstarch slurry (1 tbsp cornstarch mixed with 2 tbsp water). Stir continuously until the sauce thickens and becomes glossy, coating the back of a spoon.

Combine and finish: Return the seared beef to the skillet, tossing to coat each piece in the thickened glaze. Cook for an additional 2-3 minutes until the beef is fully coated and warmed through.

Serve: Garnish with chopped green onions and serve hot over steamed rice or noodles.