Heat 2 tablespoons of olive oil in your large skillet or pot over medium-high heat. Add 1 pound of ground beef, breaking it apart with your spoon. Cook until browned and no longer pink, about 5-7 minutes. Season with a pinch of salt and pepper. Once browned, transfer the beef to a bowl and set aside, leaving the rendered fat in the pot.
In the same pot, add the diced onion and bell pepper. Sauté for about 4-5 minutes until softened. Toss in the minced garlic and cook for an additional minute until fragrant, stirring constantly to prevent burning.
Return the browned beef to the pot. Sprinkle in the 2 tablespoons of Cajun seasoning, stirring well to coat the meat and vegetables evenly. Pour in the entire can of diced tomatoes with their juices and the 2 cups of beef broth. Stir to combine everything.
Add the 8 ounces of penne pasta directly into the pot. Give it a good stir to submerge the pasta in the liquid. Bring the mixture to a boil, then reduce to a simmer. Cover with a lid and let cook for about 12 minutes, stirring occasionally to prevent sticking, until the pasta is tender and has absorbed most of the liquid.
Once the pasta is cooked, stir in 1 cup of heavy cream. Let it simmer uncovered for 2-3 minutes until the sauce thickens slightly. Remove from heat and mix in the 1/2 cup of grated Parmesan cheese until melted and creamy. Adjust seasoning with additional salt and pepper if needed.
Sprinkle chopped fresh parsley over the pasta for a pop of color and freshness. Serve immediately, and enjoy the rich, spicy, and creamy goodness of your One-Pot Creamy Cajun Beef Pasta.