Add the lemongrass and cinnamon to the oil left in the frying pan. Cook briefly. Deglaze the pan with the chicken stock. Return the chicken to the pan, lower heat, cover, and cook until tender, about 25 minutes.
Remove the chicken from the frying pan and set aside. Keep warm. Strain the cooking liquids back and return them to the frying pan. Discard the cooked lemongrass and cinnamon. Add the lemon juice to the sauce and reduce by about half.