Preheat the oven to 180C, fan-forced. Line 2 oven trays with baking paper. Finely chop the rosemary leaves, discarding the stems. Crush or finely chop the garlic. Combine the rosemary, garlic, mint and garlic seasoning, 1 tbs wholegrain mustard and 1 tbs extra virgin olive oil in a large bowl and season with salt and pepper. Add the lamb and turn to coat.
Step 2 — Prep and roast potato
Cut the unpeeled potatoes into 4cm chunks. Put the potato on a lined tray, drizzle with 2 tsp extra virgin olive oil, season with salt and pepper and toss to coat. Spread in an even layer and roast for 35 mins or until tender.
Step 3 — Prep ingredients
While the potato is roasting, trim the beans. Pick the mint leaves, discarding the stems.
Step 4 — Cook lamb
Preheat a chargrill pan over high heat until hot. Cook the lamb, turning regularly, for 4 mins or until browned. Transfer to the remaining lined tray. 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.
Step 5 — Make mint sauce
Meanwhile, bring a small saucepan of water to the boil for the beans. Put the mint, 2 tbs apple cider vinegar, 2 tbs brown sugar and 3 tsp extra virgin olive oil in a tall jug. Blend with a stick blender until almost smooth. Season with salt.
Step 6 — Get ready to serve
Add the beans to the pan of boiling water and cook for 3 mins or until tender. Drain. Return to the pan, add 1 tsp extra virgin olive oil, season with salt and pepper and toss to coat. Slice the lamb. Divide the lamb among plates and drizzle with any resting juices. Serve with the mint sauce, beans and potato.