Many varieties
Considering how simple lentil soup is, there are surprisingly many schools for how to make it.
The most obvious is the color. Some are yellow, others almost completely red. I thought for a long time that these soups were made on different lentils. It is true that some people also make soups on yellow lentils, but this is also the natural color of red lentils when cooked to pieces. The red color comes from tomato puree, not the lentils.
Fluid is another contentious issue. Chicken power gives more flavor, but can quickly drown out the good taste of lentils. If you use water, you get a lighter soup, which is also easier to make. Thus, it is perfect to make on a normal weekday.
Also it was this with dining. A squeeze of lemon is mandatory. The Turks like to have over a spoonful of mild chili butter. In Egypt, both croutons and caramelized onions are common. I do like the Turks, but I love herbs as I am, I also like to sprinkle some fresh, freshly chopped parsley on top.
The common denominator
All these ways of making lentil soup still have something in common: They are all crispy good, and easy to make. The recipe below is a basic recipe, a classic variant as you like to get it in corner cafes around the Middle East, served with good bread.
You can make yours exactly the way you want.