Heat a pan and add the coconut oil. When the oil is hot, add the mustard seeds, urad dal, chana dal, and hing. When the mustard seeds splutter, add green chilies, curry leaves, and onion.
Cook until the onions are soft and translucent. Now add the turmeric powder and salt. Mix well and cook for a minute.
Next, add the crumbled idli pieces.
Mix them thoroughly and in medium-low flame, let it cook for 5-7 minutes till it forms the light brown crust. (This is optional) You can cook for 3 to 4 minutes over medium heat and turn off the heat as well.
Adjust the salt and green chilies to taste.
Along with green chilies, you can add up to 1 tsp of chopped ginger and two garlic cloves, chopped as well.
You can use grated carrots, cabbage, and peas (or veggies of your choice) to make a veggie-loaded upma. Make sure you cook the veggies thoroughly before adding the idli.
I have used my cast-iron pan for making this idli upma. If you have a cast-iron pan, I would recommend that for making this upma. After adding the crumbled idlis, I mix and cook the idlis over medium-low heat for 5 to 7 minutes till it forms the light brown crust.
Make sure your idlis are cool and dry. I don't crumble the idli like cornmeal. I crumble them roughly.