Place the rice in a sieve and rinse under cold running water until the water runs clear.
Place the rice in a large saucepan with the chicken stock and bring to the boil. Simmer for about 10 minutes.
Add the sliced chicken to the pan and simmer, partly covered, for a further 5 minutes. Stir in the spinach and continue simmering for another 5 minutes or until the rice is tender and the chicken and spinach are cooked.
Season with the lemon juice and pepper, then serve hot.