Wash the lentils and cook them in a saucepan with four times their volume of water for 20 minutes or until soft.
Near the end of the cooking time, add the bulgur wheat and cook for 2 more minutes.
Turn off the heat and allow to stand for 20 minutes. Drain any excess of water.
In a frying pan, heat up some oil and fry the onion until translucent, add the tomato purée and remove from the heat.
Add the remaining ingredients (except the limes and lettuce) and allow to cool down.
Shape the mixture. Put over some lettuce leaves and serve with lime slices.