Toast the coriander, turmeric, cumin seeds, fennel seeds and cayenne in a dry skillet over high heat until fragrant, 2 to 3 minutes. Pour the oil into a large mixing bowl, and then add the toasted spices. Add the ginger, cauliflower, chickpeas and onions, and toss to coat everything evenly. Place on a sheet tray and season with salt and pepper. Roast in the oven until browned and the cauliflower is tender, 30 to 35 minutes. Serve with cilantro sprigs and finish with a squeeze of the fresh lime juice.