Form chicken into balls about 1 inch in diameter. In saucepan, bring stock to a boil and drop in the chicken balls. Add rice and season with fish sauce. Cook until chicken balls are firm no more than 10 minutes. Take the pan off of the heat and stir in lettuce, ginger and green onions. Add msg and black pepper. Saute garlic in oil until light brown. Sprinkle over the top of the soup and serve.