In a bowl, marinate the chicken with garlic, black pepper, soy sauce, sugar, oyster sauce and half of the chopped spring onion for at least 30 minutes.
In a pan or wok, heat the 2 Tbsp. oil over medium-high heat.
Add the marinated chicken and stir-fry until lightly browned.
Add the marinade without the aromatics in the pan and bring to a boil.
Stir until the marinade is reduced. Add butter and stir until the butter is melted. Cover and simmer for 5 minutes.
Uncover and stir fry until the chicken is cooked.
When cooked, Transfer to a serving dish and garnish with toasted garlic and chopped spring onions.
Serve hot with cooked rice or noodles.