Heat the oil with 1/4 cup of the butter in a skillet. Add the chopped onion and garlic, and fry for a couple of minutes. Add the mushrooms and cook a little longer. Add the parsley, mint, chives, thyme, lemon juice, salt and pepper, and bread crumbs and fry until the crumbs begin to brown. Remove from the pan and set aside. Remove the bone from the chops, place into the skillet, and sear both sides.
Work with 3 (8 by 8-inch) sheets of phyllo pastry at a time (if they are bigger there is too much overlap), and cover the rest with a damp cloth to prevent them from drying out. Melt the remaining 1/4 cup butter. Brush each sheet with melted butter before covering with the next sheet. When you have buttered 3 sheets, place a lamb chop in the middle, add a quarter of the mushroom stuffing, and fold the phyllo pastry over to make a parcel. Repeat with the remaining lamb chops and phyllo pastry. (When you are making the parcel make sure the ones you have done remain covered with a damp cloth.)
Preheat the oven to 400 degrees F.
Put the parcels on a baking sheet and cook them in the oven for 10 minutes. Reduce the heat to 325 degrees F and cook for a further 30 minutes or until pastry is golden brown.