In a saucepan, add the moong dal and bring to the boil over a medium heat. leave to boil for around 20-30 minutes or until soft and cooked through. Set aside.
Put the beets in a small saucepan of boiling water over a medium heat.
Boil for around 15-20 minutes or until a knife can be inserted into the beet very easily.
Once boiled, remove the beets and put them into a bowl of cold water to cool them down.
Once cooled, peel the beets and grate them finely. Set them aside.
In a large saucepan, add the oil. Place over medium high heat and add the seeds. Toast gently for a minute until the mustard seeds start to pop then immediately add the onion and garlic. Fry for a few minutes until the onion is turning translucent. Add the chilli, fry for a minute.
Add the grated beetroot and stir. Add the spices the salt and the lentils, along with the stock.
Cover and let simmer for around 10 minutes or until the sauce is nice and thick. Right before serving, stir in the lime juice.