In a bowl, combine the thinly sliced flank steak with soy sauce, sesame oil, salt, and pepper. Let it marinate for about 15-20 minutes.
After marinating, sprinkle the cornstarch over the beef slices, ensuring they are well coated.
In a large frying pan or wok, heat enough vegetable oil over medium-high heat to cover the bottom of the pan.
Carefully add the coated beef slices to the hot oil in batches. Fry until golden brown and crispy, approximately 3-4 minutes per side. Remove and drain on paper towels.
In the same pan, remove excess oil but leave a tablespoon. Add the minced garlic and ginger, sautéing for about 30 seconds until fragrant. Then, add sliced bell peppers and stir-fry for 2-3 minutes until they are tender-crisp.
Add the crispy beef back to the pan. Stir in chili paste and honey, mixing everything well until evenly coated. Cook for another minute.
Toss in the chopped green onions, and give a final stir. Taste and adjust seasonings as needed.
Transfer the crispy chilli beef onto a serving plate and garnish with sesame seeds on top.
Notes
Adjust chili paste according to your spice preference.