Make the Idli Batter: Soak urad dal & fenugreek seeds in a bowl and idli rawa in another bowl for at least 4 hours. Grind dal into a smooth paste. Drain and squeeze the water from the rawa and add it to the dal along with salt. Mix well and set the batter aside to ferment in a warm place for 8~12 hours.
Make the Veggie Mixture: Microwave potato and carrot until tender. Alternately they can be boiled or steamed also.
Grind the coconut, roasted gram, green chilies and cilantro into a smooth paste.
Heat 2tsp oil in a saute pan; add mustard seeds, urad dal and curry leaves; once the seeds start to splutter add onions and cashews. Cook till the onions turn translucent.
Next add tomatoes and the other cooked veggies. Cook until tomatoes turn mushy.
Add the masala paste and salt. Mix well and cook for 2 minutes. Turn off the heat and let cool for a few minutes.
Then add this mixture to the idli batter. Mix well and distribute the batter evenly in the idli molds, steam for 12~15 minutes. Serve hot with chutney of choice.