Wash the lentils and cook them in a pan with four times their volume of water for 20 minutes, or until soft.
Near the end of the cooking time add the bulghur wheat and cook for two more minutes.
Turn off the heat and allow to stand for 20 minutes. Drain any excess water.
In a pan, fry the onion in the olive oil, add the tomato purée and remove from the heat.
Add the remaining ingredients (except the lettuce) and allow to cool
Shape the mixture into walnut-sized balls (using your hands) and serve on a bed of lettuce.