Cut the chicken into thin slices. Core the pepper and cut into bite-sized pieces. Cut the chilli pepper into oblique rings. Peel and quarter the onion.
Fry the chili paste (Nam Prik) in a hot wok and deglaze with the chicken stock. Bring to the boil again. Add the bell pepper, onion and chicken. Cook the chicken in 2-3 minutes. Now add the fish sauce, sugar, oyster sauce and chilli pepper and bring everything to a boil. Just before serving, stir in the basil.