Mix the shredded meat, cheeses and soup
Place in crockpot and warm on low for 2 to 3 hours ~or~ if you're in a hurry just mix it up in a skillet, cover and warm over very low heat for 20 to 30 minutes
In a separate skillet caramelize your onions in a bit of butter or beef broth
Cut the rolls in half and place them on a foil-lined baking sheet
Top the bread with the meat mixture, then the onions, then the cheeses.
Place under the broiler for about 5 minutes to melt the cheese.