Heat oven to 200C/180C fan/ gas 6. Pop the breadcrumbs, lamb mince, egg and plenty of seasoning in a bowl. Grate in half an onion and sprinkle in half the chopped mint. Give everything a good mix and shape into 8 patties. Place on a large, shallow roasting tray.
Cut the remaining onion halves into wedges. Place them on the tray around the lamb patties with the potatoes, courgettes and cherry tomatoes. Drizzle with olive oil and season. Bake for around 40 mins, turning everything once, until the lamb is cooked though and the vegetables are tender. Remove from the oven and sprinkle with feta and remaining mint.