Heat oil in a large pan or wok, cook the fishballs, stirring constantly to avoid burning. Remove fishballs from pan and set aside.
Add more oil if necessary. Saute garlic and onion in the same wok until soft. Add the mashed sardines with the sauce. Stir for about two minutes.
Add the chicken stock (from boiling the chicken) and let boil. Add the noodles. Lower heat, stir and combine ingredients and cook until noodles are soft and the liquid has been absorbed. Add water or chicken stock if needed. Add the fishballs and season with salt and pepper.