Heat olive oil in a large pot or deep skillet over medium-high heat.
Add ground beef and cook, breaking it apart with a spoon, until browned and cooked through, about 5-7 minutes.
Add diced onion and minced garlic to the pot and cook until the onion is softened, about 3 minutes.
Stir in diced tomatoes with their juice, beef broth, uncooked penne pasta, dried Italian seasoning, salt, black pepper, and crushed red pepper flakes.
Bring the mixture to a boil, then reduce heat to medium-low and simmer uncovered, stirring occasionally, until the pasta is tender and most of the liquid is absorbed, about 15-18 minutes.
Remove the pot from heat and stir in grated Parmesan cheese until melted and combined.
Garnish with chopped fresh parsley before serving.