Soak the moong dal in water (room temperature ) for 2 hours or minimum of half an hour depending on how quickly they soften. Drain water through a colander.
Wash the sago well. Drain. Pour boiling water on sago enough to cover it. Close the vessel with a lid and set aside for 15 mins. Drain water through a colander. Sprinkle with the rice flour to separate the grains.
Heat oil in a heavy bottomed pan. Add the mustard and cumin and let crackle. Add the asafoetida, chopped onions, green chillies, ginger and fry till the onions soften.
Add the curry leaves and sauté for 30 seconds. Add the drained sago and dal, salt, sugar. Cover and cook on low flame till both the sago and dal are cooked. Stir in between to prevent ingredients from sticking to the pan. You can sprinkle more oil if necessary.
May take from 8 to 10 mins to cook them depending on how soft the sago and dal were when soaked.
Adjust seasoning. Add the crushed peanuts, lime juice. Mix once, garnish and serve hot.
NoteIf unsure if the dal will cook well along with sago, you could cook the dal separately till it is just tender. Drain. Squeeze the excess water when it cools down a bit. Add it to the pan after the sago is cooked. Then add the lime juice and peanuts.
Adding moong dal is optional. You could add some vegetables instead.
You could also add 1 to 2 boiled, peeled and cubed potatoes. If adding potatoes, add after the sago and/or dal is cooked. Add the potatoes along with lime juice.
You could add peeled and grated carrots. If adding, add after the onions are translucent. Fry the carrots for a minute or two and then add sago.
May add 2 tbsp grated coconut instead of peanuts.
The soaked and drained sago before adding to the pan should separate easily without sticking to each other. Hence some rice flour is added to soak excess moisture. You could add a tbsp of besan/ gram flour instead. Do not add flour more than the specified amount.
You could apply oil on the insides of the pan completely before doing the upma to prevent sticking.