Combine the marinade ingredients in a bowl. Slice the lamb finely but roughly at different angles. Add the lamb to the bowl and turn to coat. Leave to marinate for at least an hour until ready to cook.
Heat a non stick frying or griddle pan and sear the lamb over a high heat, tossing it in the pan until crisped on the edges but still a little pink inside. Add the oregano and thyme and toss well.
Heat the pitta in a warm oven or dry frying pan for 3 minutes. Place a pitta on each plate, add a spoonful of yoghurt, pile the lamb on top and scatter over the feta.