Preheat oven to 150ºC (300ºF). To make the minted yoghurt, combine the yoghurt, mint, lemon juice, cumin and pepper and set aside.
Place the lamb in a bowl with the oil, salt and pepper and toss to coat. Heat a non-stick frying pan over high heat. Cook the lamb for 2 minutes each side and set aside. Place the tart shells on a baking tray and bake for 8 minutes or until golden and crispy. Slice the lamb and place one slice in each tart shell. Spoon 1 teaspoon of minted yoghurt onto the lamb and top with mint to serve. Makes 24.