Mix the panko bread crumbs and milk in a small bowl. Set aside. (You can use regular bread crumbs if you don't have panko.)
Mince 1/2 of a yellow onion and put in a large bowl.
Mince 2 cloves of garlic and add to the bowl.
Add the ground beef to the bowl and mix it all together with your hands.
Add the Italian seasoning and a sprinkle of salt and pepper to the meat mixture, and combine with your hands.
Beat the egg in a cup and add it to the meat mixture, combining with your hands.
Do I need to tell you to wash your hands?
Add the milk and bread crumb mixture and combine with your hands.
Pour in the grated Parmesan and mix with your hands until combined.
Spray a baking dish lightly with cooking spray.
Form meatballs. Mine are a bit larger than a tablespoon.
Pour the sauce evenly over the meatballs.
Cover with aluminum foil and bake for 45 minutes. Meatballs are fully cooked when a thermometer placed in the center registers 160 degrees.
A few minutes before the meatballs are done, slice Italian bread into hero sized lengths (that can be according to your preference) and then slice them open.
Remove the meatballs from the oven.
Set your oven to broil and move the rack closer to the top shelf.
Remove the foil and place slices of mozzarella cheese on top of the meatballs. You can put as much as you like, but I placed one slice for 1.5 meatballs. My cheese is for cheaters, the pre-sliced kind.
Return the uncovered meatballs under the broiler, surrounding the dish with the sliced bread so it can toast.
Broil until the cheese melted and bubbly and the bread is toasted. Keep an eye on the bread!
Carefully plate your heroes: bottom bread, meatballs with sauce and cheese, top bread.
A knife and fork will definitely help you to eat this delicious mess!
Notes
You can find a recipe for my homemade Italian seasoning on the post for my focaccia bread or just buy it pre-made.