Preheat the oven to 400 degrees F. Whisk together the mayonnaise, lemon juice and cayenne in a small bowl, and season with 1/4 teaspoon each salt and pepper; set aside.
Lay the Canadian bacon flat on a baking sheet. Generously spread both English muffin halves with the butter, sprinkle with some salt and pepper and transfer to the baking sheet. Bake until the muffins start to crisp and the bacon is fragrant, about 10 minutes. Top the bacon evenly with the spinach, and continue baking until the spinach is wilted and the muffins are nicely browned, about 5 minutes.
Meanwhile, heat the vegetable oil in a small skillet over medium-high heat. Crack the egg in the skillet, sprinkle with salt and pepper and cook until the egg white is set and crispy on the bottom and edges and the yolk is still runny, 2 to 3 minutes.
Arrange 1 spinach-topped slice of Canadian bacon on 1 English muffin half, top with the egg, drizzle with the mayonnaise mixture and top with the remaining spinach-topped bacon slice and muffin half.
Copyright 2015 Television Food Network, G.P. All rights reserved.