This soup is loosely based on this recipe from Melissa Clark in the NY Times. I say loosely, because I didn't stick to the quantities, omitted the cilantro, and added some crushed coriander seed.
For the carrots, I used my veggie peeler to get thin strips, then chopped those up. That's probably the best idea I've ever had for soup - no matter how small you dice carrots, you always get chunks of carrot. The peel and chop method worked perfectly, giving the carrots the same consistency as the lentils. (Definitely use red lentils, also called masoor dal, any other kind won't break down enough.)
Since all the veggies were really small already, I didn't use a blender (immersion or otherwise), just mashed with a spoon until it was slightly thicker.
If you haven't tried lemon juice in soup - not just lentil, it works in chicken too, and would probably work in a beans & greens soup - I strongly urge you to go out and buy a lemon.