Make cheese sauce by melting butter in a medium pot, then blending in flour. Stir in remaining ingredients. Cook and stir until thickened, then add shredded cheese, mix in well, and remove from heat.

At the same time, begin scrambled eggs by melting butter in a large pan. Add green onions and mushrooms to the pan, cook until softened, then pour beaten eggs over top. Scramble over medium heat until eggs are cooked through.

Spread scrambled egg mixture evenly over the bottom of a 9 x 13 casserole pan.

Pour the cheese sauce as evenly as you can over the scrambled eggs, using it all up.

Combine toasted bread crumbs with melted butter. I find the easiest way to do this is to use the hot pan from the scrambled eggs after they've been taken out, melt the butter in it, then add the crumbs and mix it around for 30 seconds. Take this mixture and add it as the final layer to the casserole.

Bake uncovered at 325 F for 45-60 minutes.