Preheat oven to 350 degrees. Spray a 9" square glass baking dish with nonstick spray.
Whisk flour and milk together until smooth. Add eggs, butter, and salt, whisking until combined. Add scallions and Canadian bacon and pour into prepared baking pan.
Bake 25 minutes in preheated oven.
Remove from oven and turn off the heat. Immediate sprinkle spinach over the top of the dish, then top with shredded cheese. Replace in warm oven and let melt, approximately 5 minutes. Cut in quarters and serve.