In a bowl, put the corn starch and toss in the chicken fillet to coat with the cornstarch.
Heat oil in the non-stick wok and stir fry the chicken for 5 minutes. Turn off heat and remove the chicken from the wok and put in an bowl and set aside.
Heat the same wok and another teaspoon of oil. Then add in the garlic, onion, spring onion, red pepper, ginger and stir fry for a few seconds then add in the vinegar, soy sauce and sugar. Stir again and simmer for a few seconds or until sugar is dissolved.
Return the chicken in the wok and stir until well coated with the sauce. Add in the peanuts and stir occasionally. Cook for a minute then turn off heat. Transfer to a serving dish and garnish with spring onions. Serve hot with steamed rice.