Preheat the oven to 425 degrees F. Lightly coat two baking sheets with cooking spray (see Note below).
In a large bowl, combine the sweet potato, cauliflower, carrots, turnip and onion. Pour in about ¾ of the olive oil and toss to coat.
In a small bowl, stir together the turmeric, ground coriander, chili powder, kosher salt, garlic powder and ground ginger. Sprinkle about ¾ of the mixture over the vegetables and toss to coat.
Place the chickpeas in another bowl and toss with the remaining olive oil and spice mixture.
Divide the vegetables between the two baking sheets and roast for 15 minutes. Divide the chickpeas between the baking sheets and stir to mix with the vegetables.
Switch the position of the baking sheets on the oven racks and cook for an additional 10 minutes, or until the vegetables are tender.
Divide the spinach between 4 bowls, then top each with the roasted vegetable/chickpea mixture and 1 ½ tablespoons dressing. Serve.