For the green herb dressing, place the herbs, spring onions, garlic, lemon zest and chilli flakes in a food processor and roughly chop. With the motor running, slowly drizzle in the olive oil and lastly the vinegar. Season with salt. Store in a screw-top jar in the fridge until needed.
Heat a barbecue grill until hot. Rub the lamb rumps with olive oil and place on the hot grill. Grill for 10 minutes, turning once, for pink lamb. Place on a warmed plate, season with salt and freshly ground black pepper, cover loosely with foil and a clean tea towel and leave to rest for 10 minutes while you barbecue the vegetables.
Lower the heat on the barbecue grill to medium-hot. Place the carrots in a large bowl with the olive oil. Season and toss well to coat. Grill, turning regularly, until tender or cooked how you like them. Remove and place on a serving plate.
Add the asparagus to the bowl and toss the spears in any remaining seasoned oil in the bowl. Place on the grill and grill until tender, 2-3 minutes for thin spears. Remove and add to the carrots. Squeeze over lemon juice to taste. Top with the rocket leaves, shredded mint and hazelnuts.
To serve, slice the lamb rump across the grain for tender meat and arrange on the vegetables. Drizzle with some of the green herb dressing and serve the remainder in a small bowl for passing around.