Red lentils are hulled and split. They cook much faster than other lentils and don’t hold their shape as well, which creates a thick soup.
In a large pot, heat the oil over high heat. Add the onion and garlic and saute until golden, about 4 minutes.
Stir in the tomato paste, cumin, salt, black pepper and chili powder, and saute for 2 minutes. Add the stock, 2 cups of water, lentils, carrots, cabbage and celery. Bring to a simmer, partially cover the pot and turn the heat to medium low. Simmer until the lentils are soft, about 30 minutes. Taste and add salt if necessary.
Puree half the soup in a blender or food processor and return it to the pot; it should remain somewhat chunky. Just before serving, stir in spinach, lemon juice and cilantro. Serve drizzled with additional olive oil.
IMPORTANT! Always use great caution when pureeing hot liquids. If you have time, allow the soup to cool before blending. Never fill the container more than half full and cover the lid with a folded kitchen towel and hold it in place before you turn on the blender. The initial surge of the blender's contents can cause the lid to pop open, possibly scalding you if still hot and certainly making a mess of your kitchen. (Recipe #709)