Preheat your oven to 375°F (190°C).

In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, garlic, salt, and pepper. Mix until well combined.

Shape the mixture into golf ball-sized meatballs and place them on a parchment-lined baking sheet.

Bake for 25-30 minutes until golden brown and cooked through.

Meanwhile, heat olive oil in a saucepan over medium heat. Sauté onion until translucent, then add crushed tomatoes with salt and pepper. Simmer for about 10 minutes.

Add the baked meatballs to the sauce and let them soak for five minutes before serving.