Heat a pan on medium flame, add oil. Once hot add mustard seeds, allow it to sputter.
Next add in the urad dal, green chillies, ginger, curry leaves and asafoetida. Sauté for a 30 seconds.
Add onions, little salt and add in the turmeric powder and cook for a few minutes until the raw turmeric flavour is gone and the onions turn translucent.
Measure and water, bring it to a boil. Check the water for salt, it has to be a tad bit salty.
Add the roasted sevai or vermicelli. Cover and cook for 10 minutes or until the water is absorbed.
Turn off the flame and add the lemon juice and mix well.