Preheat your oven to 400°F.
In a large mixing bowl, combine the ground beef, ricotta cheese, Parmesan cheese, breadcrumbs, egg, garlic, oregano, salt, black pepper, and parsley. Mix until just combined; do not overmix.
Using your hands, form the mixture into meatballs, about 1.5 inches in diameter. Place the meatballs on a baking sheet lined with parchment paper.
Drizzle the olive oil over the meatballs and 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 with the marinara sauce and simmer for an additional 5-10 minutes to allow the flavors to meld.
Serve the meatballs hot, garnished with fresh basil leaves if desired.