Preheat your oven to 400°F.
In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, milk, egg, garlic, oregano, salt, black pepper, and red pepper flakes. Mix until just combined; do not overmix.
Shape the mixture into meatballs, about 1 to 1.5 inches in diameter.
Place the meatballs on a baking sheet lined with parchment paper.
Drizzle olive oil over the meatballs.
Bake in the preheated oven for 20-25 minutes, or until cooked through and browned.
While the meatballs are baking, heat the marinara sauce in a large skillet over medium heat.
Once the meatballs are done, transfer them to the skillet and simmer in the sauce for an additional 5-10 minutes.
Serve warm with spaghetti, on a sub roll, or over rice.