Season the chicken thighs with black pepper.
In a bowl, mix the plum sauce, oyster sauce, sweet soy sauce, and fish sauce together.
Preheat an air fryer to 200°C. Place the seasoned chicken in the air fryer and cook for 20 minutes until golden brown.
Chop 6 large cloves of garlic, 1 onion, and 4 dried red peppers finely.
In a wok or pan, sauté the chopped ingredients until they start to soften.
Add water as needed to prevent burning. Be cautious during cooking.
Mix in the plum sauce mixture and bring it to a simmer.
Add sliced lemongrass, dried chili peppers, and five-leaf coriander leaves for aroma.
Place the cooked chicken into the wok with the sauce and cook until well-coated and heated through.