Meatballs: Add 1 tablespoon olive oil over medium heat in a medium pan. When the oil is shimmering, add diced onions and cook for about 8 to 10 minutes until the onions are soft.

After 8 to 10 minutes add garlic, stir it in with the onions, and cook for another two minutes. Remove pan from heat and allow garlic and onions to cool in a large bowl.

Preheat oven to 400 degrees F (205 C).

In the large bowl with the garlic and onions, combine all Meatball ingredients. With clean hands, mix everything together so that all ingredients are combined very well with the ground beef.

Again, with your hands, pull off hunks of the ground beef mixture and roll them into balls that are about 1.5 inches across. With 2 pounds of meat, you should end up with 20 to 24 meatballs. 

Add all meatballs to a parchment-lined sheet pan, leaving some space between each meatball. 

Once the oven has reached 400 F, cook the meatballs for 20 minutes.

Sriracha glaze: while the meatballs are cooking, add all sriracha glaze ingredients into a small bowl. Whisk to combine fully.

Once the meatballs have cooked for 20 minutes, remove the pan from the oven, and with a kitchen brush or a spoon, add some sriracha glaze to each meatball. Once they have all been glazed add the pan of meatballs back to the oven and cook for an additional 5 to 10 minutes. If you have a digital thermometer, you want to ensure the meatballs get to 160 degrees F to be completely cooked through. 

If you are making meatball subs immediately, leave your oven on so that you will have an opportunity to melt the cheese.

Sandwich assembly: if your meatballs are cold when you are making this sandwich, you will need to preheat your oven to 350 degrees F (176 C). 

Slice a bread roll lengthwise 2/3rds of the way through the bread and carefully open the roll up like a hinge. You can remove some of the interior bread at this point if you would like the meatballs to tuck into the bread a bit more. This is optional though. 

Add 3 meatballs for every six inches of bread, top with more sriracha glaze and top the meatballs with slices of cheese. Close the sandwich and add each meatball filled sandwich to a sheet pan.

If your meatballs are cold: add the pan with meatball subs to the 350-degree oven and bake for 10 to 15 minutes to melt the cheese and warm everything through. 

If your meatballs are hot: add the pan with meatball subs to the already hot oven and bake for 2 to 4 minutes to melt the cheese and warm everything through. The oven is already pretty hot, so peek at the sub from time to time to make sure nothing burns. When the cheese is melty pull it out of the oven.

Sprinkle diced parsley and parmesan cheese on the saucy parts of each sandwich. Serve and enjoy.