Heat the oil and 115g/4oz butter in a frying pan, add the chopped onions and garlic, fry for a couple of minutes, then add the mushrooms. Cook a little more, add the parsley, mint, chives, thyme, lemon juice, seasoning and breadcrumbs and fry until the crumbs begin to brown. Remove from pan and set aside. Put the chops into the frying pan and sear both sides.
Take 3x20cm/8in sheets of filo pastry (if they are bigger there is too much overlap). Cover the rest with a damp cloth to prevent drying out. Melt the remaining butter. Brush each sheet with melted butter, before covering with the next one. When you have buttered 3 sheets, place a lamb chop in the centre, add a quarter of the stuffing and fold the filo pastry over to make a parcel. Repeat with the other lamb chops. (When you are making the parcels make sure that the ones you have done are covered with a damp cloth to prevent the filo from drying out.)
Put the parcels on a baking dish and cook them in a preheated oven at 200°C/400°F/Gas 6 for 20 minutes, reduce heat to 180°C/ 350°F/Gas 4 and cook for a further 40 minutes.