In a 5- to 6-quart Dutch oven or other heavy-duty pot, heat the oil over medium-high heat. Add the onion and cook, stirring occasionally, until beginning to brown, 3 to 4 minutes. Reduce the heat to medium (or medium low if necessary) and cook until the onion is richly browned, 5 to 7 minutes more. Add the garlic and ginger; cook, stirring, for 1 minute to blend the flavors. Add the coriander, cumin, turmeric, and cayenne; stir for 30 seconds to toast the spices. Add the tomato paste and stir until well blended with the aromatics, about 1 minute.Add the broth, coconut milk, cinnamon stick, 1 tsp. salt, and 1/4 tsp. pepper and bring to a boil. Reduce the heat to medium low or low and simmer for 10 minutes. Add the cauliflower, sweet potatoes, tomatoes, and carrots. Raise the heat to medium high and return to a boil. Reduce the heat to medium low, cover, and simmer until the vegetables are tender, 20 to 25 minutes. Discard the cinnamon stick. Stir in the chickpeas, spinach, lime juice, and zest; cook until the spinach has wilted, about 3 minutes more. Season to taste with salt. Serve garnished with the cilantro.