Split and toast the English muffin until golden brown.
Coat a small non-stick skillet with cooking spray and heat over medium-low heat.
Pour the egg whites into the skillet, season with salt and pepper, and cook until firm. Fold the egg whites into a shape that fits the muffin.
Place the Canadian bacon in the skillet for 30-45 seconds per side until heated through.
Layer the cooked egg whites, cheese slice, fresh baby spinach, and Canadian bacon on the bottom half of the muffin.
Place the top half of the muffin over the fillings and serve warm.