Slice your croissants in half.
Next, grease a casserole dish and placing the croissants in it.
Toast the croissants at 350 degrees for about five minutes or until just slightly browned.
Cover the croissants with Swiss cheese (be careful the pan may be hot from toasting).
Heat the butter in a large skillet and combine the mushrooms, sandwich meat, and green onions. Saute on medium for about five minutes and then set aside to cool slightly.
Cover the croissants with the mixture. (Again, be careful the pan may still be hot from toasting your croissants).
Next, pour the egg and heavy cream mixture over the casserole and then add the remaining cheese on top.
At this point, the casserole can be kept in the refrigerator overnight for a no fuss fix the next morning or you can go ahead and bake the casserole if you're ready.
The casserole needs to covered with foil and cooked at 350 degrees for about 45 minutes then uncovered for 5 to 10 additional minutes or until the cheese is completely melted.