If you are making horse gram rasam, you will already have cooked horse gram. If not, soak 1 cup horse gram in warm water for 2 hours. Pressure cook with 2 cups of water for 6-8 whistles.
In a kadai/pan, add in 1 tsp oil. Temper with 1 tsp mustard seeds, a big pinch of asafoetida, few curry leaves, 3-4 spicy dry red chillies, 2 large onions finely chopped. Fry until onions cook well but remain crunchy.
Next, add in the cooked horse gram, salt to taste, 3 to 4 tbsp (or more) fresh grated coconut. Mix everything well.
Lastly, squeeze half a lemon, add in chopped coriander leaves. Mix well and it is ready to be served.
Notes
Always remember to press a cooked horse gram to check if it is cooked well. Otherwise, cook for some more time.
Adjust the red chillies as per your taste.
Add good amount of onions and coconut for best results.