Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

In a large mixing bowl, combine ground meat, breadcrumbs, egg, finely grated onion, and Italian seasonings.

Shape the meat mixture into golf ball-sized meatballs, making a small indentation to stuff with cheese, then seal the tops.

Place meatballs on the baking sheet and bake for 25-30 minutes until golden brown and internal temperature reaches 160°F (71°C).

Boil salted water in a large pot, cook spaghetti for about 8-10 minutes or until al dente, then drain.

Heat marinara sauce in a saucepan over medium heat for 5-7 minutes until warmed through.

Plate spaghetti, ladle warm marinara sauce over it, and place the baked meatballs on top.