Heat the oil over medium heat in a stock pot. Add onions and sauté for 3 minutes or until slightly translucent.
Add chorizo, set the heat to medium-low and cook, stirring, for 5 minutes.
Add the tomato sauce and the spices mixture, cook stirring for 2 minutes.
Add the lentils, carrots and potatoes.
Pour in the chicken stock (or water) and bring to a boil.
Cover and cook for about 25-30 minutes over medium-low heat, adding more water if necessary.
Adjust with salt and allow the soup to thick to your desired consistency (read notes).
Serve warm with homemade tortillas or bolillo bread.
3 cups of cooked lentils are about 1 ½ cups of uncooked lentils.
At the end, you can adjust the thickness of this soup by adding more water or allowing to evaporate until your desired consistency. You can even use a potato masher and mash a bit the soup, to make it thicker.