Preheat the oven to 425°. On a work surface, mash the garlic to a paste with a pinch of salt. In a large roasting pan, mix the paste with the curry powder and vegetable oil. Add the eggplant, onion, chickpeas and ginger, season with salt and pepper and toss well. Spread the vegetables in an even layer and roast for about 30 minutes, stirring once or twice, until the eggplant and onion are tender. Stir in the spinach and roast just until wilted, about 2 minutes. Serve with warm naan and yogurt.