Heat olive oil in a large pot or deep skillet over medium-high heat.
Add the chicken pieces and cook for 5-6 minutes until browned and cooked through. Remove chicken from the pot and set aside.
In the same pot, add diced onion and cook for 3-4 minutes until softened.
Add minced garlic and cook for 1 minute until fragrant.
Pour in the diced tomatoes with their juice, chicken broth, dried Italian seasoning, salt, black pepper, and red pepper flakes. Stir to combine.
Add the uncooked penne pasta to the pot and stir to submerge the pasta in the liquid.
Bring the mixture to a boil, then reduce heat to medium-low and simmer uncovered for 12-15 minutes, stirring occasionally, until the pasta is cooked and most of the liquid is absorbed.
Return the cooked chicken to the pot and stir to combine. Cook for an additional 2 minutes to heat through.
Remove the pot from heat and stir in the grated Parmesan cheese until melted and creamy.
Sprinkle chopped fresh parsley over the top before serving.