Preheat the oven to 180C, fan-forced. Line an oven tray with baking paper. Finely chop the macadamias. Peel the sweet potatoes and cut into 5cm chunks. Put the sweet potato and half the barbecue seasoning on the lined tray, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Bake for 35 mins.
Step 2 — Marinate lamb
Scatter the macadamias over the sweet potato and bake for a further 5 mins or until the sweet potato is tender. Meanwhile, crush or finely chop the garlic. Finely chop the rosemary leaves, discarding the stems. Combine the garlic, rosemary, remaining barbecue seasoning and 1 tbs olive oil in a large bowl and season with salt and pepper. Add the lamb and turn to coat.
Step 3 — Brown lamb
Line an oven tray with baking paper. Heat a medium frypan over high heat. Cook the lamb, turning regularly, for 4 mins or until browned. Transfer to the lined tray. Reserve the pan. Pour any remaining marinade in the bowl over the lamb.
Step 4 — Roast lamb
Roast the lamb for 6-7 mins for medium-rare, or until cooked to your liking. Remove from the oven and rest for 8 mins (see Kitchen 101). While the lamb is resting, bring a small saucepan of water to the boil. Add the peas and cook for 2 mins or until tender. Drain.
Step 5 — Make gravy and serve up
Put the gravy powder and 160ml (⅔ cup) water in the reserved pan over medium-high heat. Cook, stirring, for 1-2 mins until the gravy boils and thickens. Divide the lamb, macadamia sweet potato and peas among plates. Drizzle over the gravy and enjoy!
Step 6 — Kitchen 101
Resting the lamb after cooking makes the meat more tender and juicy. It's worth the wait!