Heat oil in a hot pan and when the oil gets hot, add mustard seeds. When mustard seeds start crackling, add cumin seeds, fenugreek seeds, curry leaves, green chillies, turmeric, hing, red chilli powder, goda masala and sauté the spices. Immediately add peanuts (soaked in hot water for few minutes), channa dal (soaked in water for few hours), cashew nuts, coconut pieces, radish, chopped arbi leaves and salt to taste. Stir all the ingredients well and put it on a slow flame, cover the pan with a lid and cook for about 4-5 minutes. After 5 minutes of slow cooking, remove the lid and add little water, cover and cook for another 5 minutes. Remove the lid and check if the arbi leaves are soft and tender. Add jaggery and mix well. Take a teaspoon of besan flour in a bowl, add little water and mix well. Add little tamarind juice and besan flour paste and bring to boil. (the besan flour paste will slightly thicken the gravy). Sprinkle some roasted peanut powder and mix well and switch off the flame.