In a bowl, mix chicken with soy sauce and cornstarch and marinate for 10 minutes.
Heat oil in a wok over high heat.
Add marinated chicken and stir-fry until lightly browned and cooked through.
Remove chicken from the wok and set aside.
Add garlic and ginger to the same wok and sauté for 20 seconds.
Add bell peppers and broccoli and stir-fry for 2–3 minutes.
Return chicken to the wok and add Hunan chili paste, rice vinegar, and sugar.
Toss everything well to coat with sauce.
Cook for another 1–2 minutes until glossy and hot.
Garnish with spring onions and serve immediately.