Preheat oven to 180 Degrees C
Put all the ingredients except the fish in a food processor and process till almost smooth.
Place the fish in an oiled baking dish and season. Cover in the hummus using wet fingers to create an even crust. Place in the oven for 10 - 15 minutes depending on thickness of fillet. Switch on the grill/ broiler to create a nice brown crust.
In the meantime fry the onions and spices in olive oil until onions are soft. Add the rice and lentils and stir fry until rice is soft. Season to taste
Mix the tahini paste with lemon juice and salt. Add water slowly, mixing a little at a time. The oaste will seize at first but keep mixing in a little at a time until it creates a runny sauce. Season accordingly.