De-bone and de-skin the chicken thigh fillets and chop them into 3-4cm long bite-sized pieces.
Combine the chicken pieces with 2 tablespoons of Khmer yellow kroeung paste and splash of neutral cooking oil to ensure the chicken is completely covered with the paste and then marinate in the fridge. Remove the chicken after you’ve finished prepping the ingredients below or for more aromatic flavours, marinate the chicken for a minimum of 30 minutes and up to an hour.
Stir-fry the garlic and onion in half a tablespoon of neutral cooking oil in a hot wok for a minute or two until the onion just begins to become translucent, then set aside.
Stir-fry the green capsicum and red capsicum for a minute or two until it just starts to soften but still maintains some crunch and set aside.
Add the marinated chicken to the wok, along with 2 tablespoons of Khmer yellow kroeung, the rest of the cooking oil, 4 tablespoons of fish sauce, and 1 teaspoon of sugar, and combine well.
Stir-fry for a few minutes until the chicken is just cooked. (Note: if you’re not used to stir-frying chicken, remove the largest piece and chop it in half to see if it’s cooked through. If it’s not, return it to the wok and stir-fry for another minute.)
Add the onion and green and red capsicums at the same time and stir-fry for another minute, then plate immediately.
Garnish with finely-sliced fresh kaffir lime leaves or fresh basil (Cambodian or Thai), and serve with steamed rice.