Preheat the grill to 220C. Cut the potatoes in half lengthways then cut into wedges about 2cm thick. Put in a bowl and toss with the oil, cumin, paprika and lots of salt and pepper. Spread out over an oven tray and grill, turning occasionally, for 20-30 minutes, or until tender to the point of a knife and crispy around the edges. Serve immediately with salad and guacamole or as a side dish.