Heat half the oil in a large non-stick frying pan over high heat. Add mushrooms and cook, stirring often, for 8 minutes or until the moisture evaporates. Set aside to cool for 10 minutes.
Combine mushrooms, chicken mince, green onions, egg, breadcrumbs and parsley in a bowl. Season well with salt and plenty of pepper, mix well to combine. Shape the mixture into 4 patties.
Heat remaining oil in a large non-stick frying pan over medium heat, alternately preheat barbecue flat plate on medium. Add the patties and cook, for 4 minutes on each side or until just cooked through.
Spread the bun bases with dijonnaise, top with tomato, salad leaves and chicken pattie. Serve.