Preheat oven to 350 degrees. Coat a muffin tin with cooking spray.
Cut off crust and flatten bread with a rolling pin. Spread a teaspoon of butter on one side of each bread slice. Press bread, buttered side down, into 2 muffin cups. The top of the bread does fan out a little. Just be sure you create enough room to add the scrambled eggs. Bake at 350 for 12-15 minutes.
In the meantime, in a medium nonstick pan, add bacon. Cook on each side until browned and crispy. Drain fat and set bacon aside on paper towels.
In the same pan, add egg whites and scallions. Crumble in cooked bacon and scramble egg whites until eggs are completely set. Add a little salt and pepper, if desired.
Divide and spoon into bread cups and serve with a fork and knife.