Heat a non-stick soup pot or Dutch oven over high heat. When the pan is very hot, all at once add the onion, garlic, cumin, coriander, and paprika. Let sit for 30 seconds without stirring, then add 1/4 cup of the chicken stock. Saute over high heat, stirring, for 4 minutes. Add another 1/4 cup of the chicken stock and scrape the bottom of the pot. Add the lentils and spinach and cook, stirring, for 2 minutes. Add the remaining 5 1/2 cups of chicken stock and the tomatoes and bring to a boil. Reduce the heat to low, season with salt and pepper, and simmer, covered, until the lentils are tender, about 50 minutes. Season with the lemon juice and additional salt and pepper, if needed. Let sit for 5 minutes before serving.
Serving Ideas : Serve with a good dense hearty bread.