Preheat oven to 425° F. Heat a skillet over medium heat.
Add Panko to hot pan and cook for 2 minutes or until toasted, stirring frequently. Remove from heat and place into a shallow dish (a pie plate works great).
Cut mozzarella sticks into 1-inch pieces.
Crack egg into a small bowl and whisk to combine.
Working with one piece at a time, dip cheese bites into the egg and then dredge in panko.
Place coated cheese onto a baking sheet coated with cooking spray.
Bake for 3-5 minutes until the cheese is softened and heated through. (Be careful not to overcook or the cheese will completely melt!)
Serve spaghetti/marinara sauce on the side for dipping.