Heat oil in a large stockpot over medium heat. Add onion and leek and cook until softened. Add carrots, celery, garlic, zucchini, chili powder, cumin, smoked paprika, and turmeric. Cook for 3-4 minutes to develop flavor, being sure to stir to prevent sticking at the bottom of the pot. Add tomatoes, lentils, cilantro and vegetable stock. Bring to a boil, then reduce heat to low and simmer, covered, until lentils are soft, 25-30 minutes. Add chopped kale and cook just until tender, about 3-4 minutes. Season to taste with salt and pepper.