Place half of your beef in the bottom of your 6-quart crock pot (I used Cera, my 6 Quart Crock Pot with Ceramic Coated Pot) and top with half of your mushrooms and half of your onion, repeat layer
Pour your soup on top of everything
Cover and cook on low for 6-8 hours
Put your stuffing mix in a bowl, top with your melted butter and 1/2 cup of liquid from your crock pot and toss (if you do not have enough liquid in your crock pot for 1/2 cup, add water to the liquid to make it a full 1/2 cup)
Pour your stuffing across the top of your beef and cover and cook on high for about 10 minutes
Spread your shredded cheese over the top of your stuffing and cover again and cook on high until your cheese is melted