Heat the olive oil to shimmering in a large soup pot. Sauté the onions and garlic for about 4 minutes. Stir in the tomato paste, cumin, chili, salt, pepper and cook a minute or two. Add the broth, water, lentils, carrots, and bring to a simmer.
Gently simmer partially covered about 30 minutes until the lentils are tender. Use an immersion blender for a while leaving the soup chunky or puree about half of it in a blender then add it back to the pot. Remember to take the center piece out of the top of the blender and cover with a wadded up kitchen towel to let the steam escape. Stir in the spinach. Add lemon juice, salt, and pepper to taste.