Spaghetti All'Amatriciana with Spicy Mozzarella Meatballs

I have been meaning to make this recipe for months but when I was deciding what to make for supper this one never seem to speak to me, well tonight it did.  This recipe was delicious and was eaten by everyone in my family, bonus!  The three different kinds of cheese in the dish made it taste really good.  They were also really good meatballs.  Perhaps the best ones I have ever eaten.

Ingredients
All'Amatriciana Sauce:
2 tablespoons olive oil
6 bacon, diced
1 yellow onion, finely chopped
2 garlic cloves, minced
Pinch crushed red pepper flakes
1 (14-ounce) can crushed tomatoes
1/2 teaspoon kosher salt, plus more for seasoning
1/2 teaspoon freshly ground black pepper, plus more for seasoning
1/2 cup grated Pecorino Romano

Meatballs:
1 small (6-ounce) onion, grated
1/2 cup chopped fresh flat-leaf parsley, plus 1/4 cup
2/3 cup grated Parmesan cheese, plus 1/4 cup
1/3 cup Italian-style bread crumbs
1 large egg
2 tablespoons ketchup
3 garlic cloves, minced
1/4 teaspoon crushed red pepper flakes
1 teaspoon kosher salt, plus more for seasoning
1/2 teaspoon freshly ground black pepper, plus more for seasoning
1 pound lean ground chicken
2 ounces  mozzarella cheese, cut into 16 (1/2-inch) cubes

1 pound spaghetti or other long pasta
Directions

For the sauce: In a large heavy skillet, heat the oil over medium heat. Add the bacon and cook, stirring constantly, until golden brown, about 5 to 7 minutes. Using a slotted spoon, remove the bacon and reserve. Add the onion and cook for 5 minutes. Stir in the garlic and red pepper flakes and cook until fragrant, about 30 seconds. Add the tomatoes, 1/2 teaspoon salt, 1/2 teaspoon black pepper, and the cooked bacon. Simmer, uncovered, over medium-low heat until the sauce thickens, about 15 minutes. Stir in the cheese and season with salt and pepper, to taste.

For the meatballs: Position an oven rack in the lower 1/3 of the oven. Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.
In a large bowl, combine the onion, 1/2 cup parsley, 2/3 cup Parmesan, bread crumbs, egg, ketchup, garlic, red pepper flakes, 1 teaspoon salt, and 1/2 teaspoon pepper. Add the chicken. Using your hands, combine all ingredients gently but thoroughly. Shape the meat mixture into 16 (1 1/2-inch-diameter) meatballs and place on the prepared baking sheet. Make a hole in the center of each meatball and place a cube of mozzarella inside. Reform the meatball so that the mozzarella is completely covered with the meat mixture. Bake the meatballs for 15 minutes until cooked through.

Bring a large pot of salted water to a boil over high heat. Add the pasta and cook until tender but still firm to the bite, stirring occasionally, about 8 to 10 minutes. Drain and place in a large serving bowl. Add the meatballs and sauce. Toss gently and season with salt and pepper, to taste. Sprinkle with the remaining parsley and Parmesan