In a soup pot, simmer the onions in 1 cup of the stock for 10 minutes.
Combine the cinnamon, turmeric, ginger, and cayenne in a small bowl and add 2 to 3 tablespoons of the hot liquid to form a paste. Stir this paste into the pot along with the carrots, celery, and the remaining stock.
Bring to a boil, then lower the heat, cover, and simmer for 5 minutes.
Add the tomatoes and potatoes and continue to cook, covered, for 15 to 20 minutes, until the potatoes are tender. Crumble in the saffron.
Stir in the lentils, chickpeas, cilantro, lemon juice, and salt and pepper to taste. Reheat and serve immediately with lemon wedges.