Peel and cut the onion lengthways, peel and finely chop the garlic, slit the red chilies lengthways and slice the tomato into four. Place a large frying pan (skillet) on a medium heat, add the vegetable oil and, when warm, add the mustard seeds, curry leaves, onion, garlic, red chilies, coriander seeds and split red gram.
Using a sieve, drain all the liquid into a bowl. Add the tamarind to the cooked pulses and blend well using a hand blender. Return the cooking liquid from the bowl to the blended pulses and bring to the boil. Serve hot with Steamed Rice.