Preheat the oven to 400 degrees. Coat a baking dish with cooking spray.
Heat the leftover marinara sauce in the microwave until warm. Pour the warmed marinara into the baking dish. Crack an egg on top of the sauce then season with sea salt and freshly cracked pepper, to taste.
Place into the oven and bake for 9-14 minutes, or until the whites set and yolk is still soft. Place the leftover piece of bread in the oven when there is 2-3 minutes time left baking for the egg. Remove from the oven and sprinkle the Parmesan and basil on top of the baked egg.
Spoon the egg and sauce onto the top of the toasted bread and serve immediately. Enjoy.