Wash the rice and urad dal seprate. Soak in water for minimum of 3 hours. Now blend them seprately and Keep covered overnight for frementing.
Next morning, mix both rice and urad dal paste to make a batter.
Heat 1 tbsp oil in a pan and fry chopped onion till onion turns pink color.
Add mustard seeds and let it splutter. Add turmeric powder, red chilli powder, ginger garlic paste, curry leaves and cook for a while. Add salt.
Add chopped vegetables now and cook till they are tender.
Mix this masala in the idli batter.
Grease the small plate with oil and fill it with the batter. Leave a scope for rising the batter, so do not overfill.
Steam cook the idli for 10 minutes on low flames. To check whether idli is done, prick a knife in idli, if it comes out clean, idlis are done.
Masala Idli is ready.
Note : For steam cooking, you can use pressure cooker if idli stand can sit in it. Pour a cup of water in cooker and keep idli stand in it. Cover the lid of cooker and take out the whistle. Now cook for 10 minutes on low flames.