Pre-heat your oven to 375 degrees F (190 C).
Place a baking sheet or cookie sheet into the oven while it is preheating. The pan being hot is helpful for the toasting process.
Melt the butter in a small bowl in the microwave for 30 to 45 seconds. Add olive oil, garlic, parsley, garlic powder, salt, and black pepper to the bowl with the melted butter and stir to combine
Using a pastry brush or spoon, paint the melted butter on both sides of all of the pieces of bread.
When the oven is heated, remove the pan and add all of the slices of bread. Put the pan back into the oven.
Cook the bread for 6 minutes, and then remove the pan from the oven and flip each slice over.
Cook for an additional 6 minutes until the toast is brown and toasted on both sides.
Remove the pan from the oven and do not turn off the heat. Add shredded mozzarella to both slices of bread.
Top one slice of bread with a large pile of cooked spaghetti and sauce. Cover with a bit of grated or shredded Parmesan cheese and place the pan back into the oven for 3 or 4 minutes or until the spaghetti is warm and the cheese has melted.
Remove the pan from the oven, close the sandwich, and serve.