Wash and drain the lentils. Put in a saucepan with 4 cups of water. 

Bring to a boil, and then simmer on medium heat until cooked (30-45 minutes).

While the lentils are boiling, heat the oil in a separate skillet, until shimmering (but not smoking).

Turn the heat down to medium. Add cumin seeds and sizzle a few seconds until aromatic.

Add sliced onions and saute over medium-low heat until soft and golden.

Stir onion-spice mixture into the boiled lentils. If the dal is too thick, add some water. It should be the consistency of a thick soup. 

Add salt to taste and simmer for 5 minutes to blend the flavors.

Serve over white rice with a side of fried potatoes or vegetable fritters.