Marinate sliced beef with beaten egg, 1 tablespoon oil, and salt for 15 minutes.
Whisk together all sauce ingredients in a bowl until smooth and set aside.
Coat marinated beef pieces evenly with cornstarch.
Heat oil in a wok or large skillet over high heat and fry beef until golden and crispy, about 3-4 minutes. Remove and drain.
Remove excess oil, leaving 2 tablespoons in pan. Stir-fry onion, bell pepper, dried chilis, ginger, and garlic for 2 minutes.
Return crispy beef to the pan and pour in the prepared sauce.
Cook while stirring constantly until sauce thickens and coats the beef, about 2-3 minutes.
Garnish with roasted sesame seeds and serve immediately over steamed rice.