Slice beef very thin, about 1/4 inch thick, cutting against the grain. Pat beef dry with paper towels to remove excess moisture.

In a bowl, toss beef strips with cornstarch, salt, and pepper until evenly coated. Shake off any excess cornstarch.

Heat vegetable oil in large skillet or wok over medium-high heat until shimmering. Working in batches, fry beef strips for 2-3 minutes per side until golden brown and crispy. Transfer to paper towel-lined plate.

In a small bowl, whisk together sweet chilli sauce, soy sauce, rice vinegar, honey, and water. Set aside.

Remove most oil from skillet, leaving about 1 tablespoon. Add minced garlic, ginger, and sliced chilli peppers. Stir-fry for about 30 seconds until fragrant.

Pour sauce mixture into skillet and bring to simmer. Let bubble for 1-2 minutes to thicken slightly.

Add crispy beef back to skillet along with sliced bell peppers and green onions. Toss quickly to coat everything in sauce, about 1 minute.

Transfer to serving plate immediately. Garnish with sesame seeds and extra green onions. Serve hot over rice or noodles.