In a small bowl, stir together the butter and garlic powder. Spread the butter evenly on the outside of each piece of bread, being sure to spread it all the way to the edges.
Sprinkle Parmesan cheese on the outside of the bread, and use your fingers or a knife to press it into the butter a bit.
Layer each sandwich in this order: bread slice (butter side out), shredded mozzarella, scoop of spaghetti, provolone cheese slices, bread slice.
Heat a well seasoned cast iron skillet or heavy non-stick skillet over medium high heat. Place the bread in the skillet and cook for about 3 minutes, or until golden brown. Carefully flip, cover the pan, and continue to cook another 2-3 minutes until the second side is brown and cheese is melted.
Remove from heat and serve immediately.