||Preheat the oven to 220ºC. Brush the lamb lightly with oil. Rub with the combined spices and then season with salt and pepper. Microwave the pumpkin and sweet potato wedges on high for 2-3 minutes to soften. Cool and pat dry with kitchen paper, place on a roasting tray lined with baking paper, drizzle or spray with oil.
||Place the lamb on a rack in a roasting dish. Roast for 15 minutes for rare, 20-25 minutes for medium, or 30 minutes for well done. For ease and accuracy use a meat thermometer. Roast the pumpkin and sweet potato alongside the lamb.
||Remove lamb, cover loosely, rest the lamb for 10 minutes before serving. While lamb is resting whisk the sour cream, rind and lime juice and lemongrass together, season with salt and pepper. Serve the lemongrass cream to drizzle over the roast pumpkin and sweet potato.