This is something that I make quite frequently.
I got the recipe from a bargain-bin book that surprisingly ended up being the one that I turn to the most out of all of my recipe books. You can find a copy of the book called "Simply: Quick and Easy"
here and I'm sure that other online bookstores have copies as well. The recipe for Dal Soup is on page ten.
I modify it by adding a half cup more red lentils, 1/8 tsb more red pepper and by cutting the tomatoes down to a single one pound can of un-drained petite-diced tomatoes.
It can be served alone or with some fluffy basmati rice and a side of naan bread.
NOM.