Place the olive oil in a 20x20cm glass baking dish. Place the chicken breasts in the dish, coating each side with oil. Squeeze the juice of 1/2 lemon over all. Slice the rest of the lemon and place a lemon slice on top of each chicken piece. Cook in the preheated oven for 30 to 40 minutes until brown.
In a large frypan, melt the 65g butter or margarine. Add the sliced mushrooms. Saute until the mushrooms are brown and have exuded their juices, about 6 minutes. Sprinkle with the flour and blend. Add the chicken stock, stirring to make a medium thick sauce. Allow to reduce, adjusting with a little more stock to make a creamy sauce. Add fresh parsley at the last minute. Spoon the sauce over the lemon baked chicken breasts. Delicious!