Fry bacon in skillet until done.
Remove to paper towels to drain.
When bacon is cool, break into small pieces; set aside.
Meanwhile, preheat oven to 350°.
Slice French bread into one-inch slices.
Lay bread slices on a cookie sheet.
Bake at 350° for 5 minutes.
Spread with butter and cut bread up into cubes. Set aside.
Drain all but 1/4 cup bacon grease.
Add mushrooms, onions and peppers and sauté a few minutes until veggies soften—about 5 minutes.
Add a handful or two of the spinach on top of the mushroom mixture and stir so the bacon grease coats the spinach.
As spinach cooks down and wilts, add more spinach until all of the spinach has been added.
This will only take a minute or two.
Remove from heat.
Stir in bread cubes, bacon pieces, salt and pepper and stir well to combine.
Spray a 9x13” glass baking dish with cooking spray.
Spread bacon mixture into prepared baking dish.
Sprinkle one cup of cheese over top of bacon mixture.
Combine eggs and milk in mixing bowl and whisk.
Pour over top of casserole.
Sprinkle remaining cup of cheese over top.
Cover and refrigerate overnight.
Bake at 350° for 45 minutes to an hour, uncovered, until cheese is melted and mixture is bubbly.