Heat Panini press or non-stick skillet over medium-high heat.
Place the spinach on 1 slice of bread. Arrange the apple slices evenly over the spinach, and sprinkle the apple with black pepper. Top with the cheese, then the remaining slice of bread.
Lightly spray the outside of the sandwich with cooking spray and place in the Panini press or skillet.
If using a skillet turn the sandwich over after about 3-4 minutes and with a spatula or a heavy skillet, press the sandwich down to mash it together. If using a Panini press, remove from the press after about 5 minutes or when the cheese is melted and the bread is light golden in color.
Serve with a small bowl of soup or salad on the side. Enjoy!