Heat oil in a large non-stick frying pan over high heat. Add the mushrooms. Cook, stirring often, for 8 minutes or until all the moisture evaporates. Remove from the heat. Allow to cool for 10 minutes. Drain excess liquid.
Combine the mushrooms, mince, green onions, celery, egg, breadcrumbs and parsley in a large bowl. Season with salt and pepper. Mix well using your hands. Shape mixture into even 12 patties.
Place 1 piece of bacon on a chopping board. Top with another piece of bacon, to form a cross. Place 1 patty in the centre and fold bacon over to enclose. Secure with toothpicks. Repeat with remaining bacon and patties.
Preheat a barbecue plate on high heat. Reduce heat to medium. Spray both sided of the patties with oil and barbecue for 5 minutes on each side or until just cooked through. Remove the toothpicks. Serve with jacket potatoes and salad.