Bring a large pot of salted water to a boil. Add penne pasta and cook until al dente, about 10-12 minutes. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add diced onion and sauté until translucent, about 3-4 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 6-8 minutes.
Stir in diced tomatoes, salt, black pepper, and dried oregano. Let simmer for 5 minutes to combine flavors.
Reduce heat to low. Stir in heavy cream and cooked penne pasta. Mix until pasta is evenly coated and sauce is creamy.
Serve pasta twirled into a neat mound in the center of shallow white bowls. Top each serving with grated parmesan cheese and a sprig of fresh parsley.