Make courgette tzatziki to go with your roast lamb. Coarsely grate 1 courgette. Toss with 1 tsp salt and pile into a colander. Squash down with a weighted plate and leave to drain for 30 mins. Stir the courgettes into yogurt with a handful of chopped mint leaves and some salt and pepper. Roast the remaining courgettes with the new potatoes and carrots in a hot oven. The potatoes will take 40-45 mins, the carrots and courgettes 30 mins.