Melt butter on stove, then add in the chopped onion ,bacon pieces and mushrooms to brown.
In a large bowl combine the breadcrumbs, egg and chicken stock , followed by the butter, onion, bacon pieces and mushrooms and the rest of the dry ingredients, mix well until combined. If not wet enough add a dash of water. Once all combined separate and roll into 4 logs to fit onto the chicken.
Slice the chicken breasts in halves to get 4 pieces, place the stuffing log in the middle then roll tightly with a rasher of bacon and hold together with toothpicks.
Place in slow cooker with 3/4 blobs of butter then cover with spinach.
cook on low 5/6 hours depending on your slow cooker.
Half way through cooking sprinkle half cup cheese over the top and do the same at last 30 minutes remaining with the other 1/2 cup cheese or can sprinkle the last lot of cheese at the end and place under grill or in oven 5/10 minutes to crisp up if preferred.
Serve with vegetable or garden salad.