Spray a stock pot with non-stick cooking spray. Saute' celery with salt until tender. Reduce heat to low and add garlic, ginger, and pepper. Cook until aromas are released, stirring constantly, about 2 minutes. Add lentils and cook an additional 3 minutes, constantly stirring so the beans are evenly cooked.
Add stock, tomato paste and spinach, bring to a boil, reduce to a simmer, and cook, uncovered, about 1 hour 15 minutes. Stir soup regularly to ensure even cooking so the beans do not burn. When done, beans should be soft inside, with no chalkiness. Puree with stick blender to desired consistancey.