Heat olive oil in a large skillet over medium heat.
Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 5-7 minutes.
Add the diced onion to the skillet and cook until softened, about 3-4 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the crushed tomatoes, chicken broth, dried oregano, dried basil, red pepper flakes, salt, and black pepper to the skillet. Stir to combine.
Bring the sauce to a simmer.
Add the rigatoni pasta to the skillet, making sure the pasta is submerged in the liquid.
Cover the skillet with a lid and cook for 15-17 minutes, stirring occasionally, until the pasta is tender and most of the liquid is absorbed.
Remove the skillet from heat and stir in the grated Parmesan cheese until melted and combined.
Garnish with chopped fresh parsley before serving.