Melt butter over medium heat in a large skillet. Saute onion & mushrooms until tender. Remove from heat to cool.
Preheat oven to 350 degrees F.
Meanwhile prepare chicken breasts for stuffing by butterflying and cutting a pocket as per THIS VIDEO.
Mix shredded cheese and parsley into the cooled mushroom/onion mixture. Sprinkle chicken with salt and pepper. Divide evenly and stuff into pocket created in the chicken. Fold as shown in the video link above.
Carefully wrap each folded breast with 2 slices of bacon, securing with a toothpick if needed. Place on a deep baking sheet or in an oblong ovenproof baker.
Bake for 45-60 minutes, depending on thickness of rolls. Chicken is done when juices run clear or internal temperature is 180 degrees C