This is a tasty, healthy, and kid-friendly soup that is easy to make. It was inspired by "Vegetarian Pleasures" by Jeanne Lemlin. See bottom of the directions for ways to improve on the kid-friendliness of this recipe.
Rinse the lentils in a strainer under cold running water (preferably filtered). Pick them over and discard any small stones. Put the water and salt in a medium-sized sauce pan. Bring to boil. Add the rinsed lentils, reduce heat and cook, uncovered, for 20 minutes stirring occasionally. Scoop off any excess foam on the top and discard.
Peel (optional) the sweet potatoes and dice into 1/2 inch pieces. Add to lentils and continue cooking.
Dice the onions and and garlic. In a small skillet, heat the olive oil, onions, garlic and spices over low heat. Cook and stir for 5 minutes or until the onions have become soft and translucent.
Add spice mix to the soup and continue to cook and occasionally stir until potatoes are tender, about 10 minutes. Add more water if soup is too thick.
Tip for kid-friendly. Reduce or don't add the garlic, onions and/or cayenne if you have a spice-sensitive kid. And if your kid is picky on texture, you can put the soup in a blender (make sure you hold the top down firmly so you don't have a hot-soup explosion) and a few ice-cubes and serve 'smooth-style'.