In a small bowl, season the egg with pepper to taste, if desired.

Place a small, nonstick frying pan over medium heat. When the pan is hot, move it away from the heat, and lightly mist it with spray. Add the egg whites. Once they begin to set slightly, use a large spatula to gently nudge them into the shape of the English muffin. Flip the egg to fully cook.

Meanwhile, toast the English muffin in a toaster or under the broiler.

Assemble the sandwich by placing the English muffin, inside up, on a plate. Top it with the cheese, then the egg, the prosciutto, and then the arugula. Serve immediately.