Preheat the Oven: Preheat your oven to 375°F to ensure the dish bakes evenly.
Cook the Pasta: Bring a large pot of salted water to a boil. Cook the penne pasta until al dente, according to package instructions. Drain and set aside.
Brown the Beef and Vegetables: In a large ovenproof skillet, brown the ground beef over medium heat. Add the mushrooms, onion, and green bell pepper about one-third of the way through the cooking process. Cook until the beef is browned, and the vegetables are tender.
Prepare the Sauce: Reduce the heat to medium-low and stir in the condensed French onion soup and Worcestershire sauce. In a small bowl, whisk together the cornstarch and cold water until smooth, then add it to the skillet. Let the sauce simmer for about 5 minutes until thickened.
Combine Pasta and Sauce: Add the cooked pasta to the skillet and gently stir until the pasta is fully coated in the sauce.
Top with Cheese and Bake: Sprinkle the shredded cheese evenly over the pasta mixture. Transfer the skillet to the preheated oven and bake for 15 minutes, or until the cheese is melted and lightly golden.
Serve: Remove the skillet from the oven and let it rest for a couple of minutes. Serve warm and enjoy!