This is a very simple lentil curry, with an irresitable Indian flavor and not too much heat. My idea of comfort food. Plus:it's no problem to get it on the table, with rice and a salad, in under an hour.
Combine the lentils, water and carrots in a large pot and bring to a boil. Reduce heat to med/low and partially cover, letting it simmer for 20 minutes.
(If you're going to cook basmati rice, start it now.) Add the potatoes, and cook for 15-20 minutes more, till the potatoes are soft. You may need to add an additional 1/2-1 cup of water if you find it getting too thick.
Meanwhile, in a small frying pan heat the olive oil (over med/high)and stir in the mustard seeds. Stir for a minute, till they start to pop. Reduce heat. Stir in the other spices and saute for 1 minute. Set aside.
When the potatoes and lentils are fully cooked, stir in the spice mixture, salt and lemon juice. Serve immediately. (With chapatis or over rice; steamed collards or salad).