Combine paprika, cumin, coriander, oregano, fennel seeds and 2 tbs of the oil in a large bowl. Add the lamb and turn to coat. Set aside for 30 mins to develop the flavours.
Meanwhile, heat a covered barbecue on medium-high. (Alternatively, preheat oven to 180°C.) Place pumpkin, zucchini, combined capsicum, fennel, onion, asparagus and peas in a large bowl. Drizzle with remaining oil. Toss to coat. Season. Cook vegetables on grill, in batches, for 1-2 mins each side or until just tender. Set aside to cool slightly.
Cook lamb on grill for 5 mins each side or until golden brown. Reduce heat to medium. Cook in covered barbecue or oven for 15 mins for medium or until cooked to your liking. Set aside, covered, for 10 mins to rest.
While the lamb is resting, to make the chimichurri, place the mint, parsley, coriander, oregano, oil, vinegar and mustard in a food processor and process until smooth. Season.
Transfer the lamb to a serving board. Thickly slice. Arrange the chargrilled vegetables on the board with radish and rocket. Drizzle with chimichurri to serve.