Mix both types of rice in a bowl, cover with plenty of water and leave to soak for about 6 hours. Also place the lentils and fenugreek seeds in a bowl, cover with water and leave to soak for the same amount of time.
Drain the rice in a fine sieve and rinse well. Purée in a blender with a little water to make a thick cream. Rinse the lentils and purée in the same way.
Mix the rice and lentil purées together, adding the salt. Cover the batter with a damp tea towel and leave to ferment for about 24 hours until it smells slightly sour and bubbles have formed on the surface.
Quarter, deseed and dice the tomatoes. Peel and dice the onions. Chop the chillies, removing the seeds if desired. Finely chop the coriander. Mix the onions, tomatoes, chilli and coriander in a bowl.
Preheat the oven to the lowest setting.
Heat a few drops of peanut oil in a large frying pan and add spoonfuls of batter to form 3 small pancakes. Fry briefly until golden, then turn over a cook the other side for 1-2 minutes.
Transfer to an ovenproof plate, cover and keep warm in the oven. Repeat until all the batter is used up. Top the warm pancakes with the onion mixture and serve with a chutney if desired.