Heat a large skillet over medium heat. Add 1 lb. lean ground beef, 1 onion (diced), 1 green bell pepper (diced), and 2 tsp garlic powder. Cook, breaking up the beef, until the beef is cooked through and the vegetables are softened. Drain any fat and return the skillet to the stovetop over medium heat.
Sprinkle 3 tbsp all-purpose flour over the beef mixture and stir continuously for about 1 to 2 minutes, until the flour is incorporated and no raw flour remains.
Stir in 1 tbsp ketchup and 3 tbsp Worcestershire sauce, scraping any browned bits from the bottom of the skillet.
Gradually stir in 3 cups low-sodium beef broth and 1 cup milk, mixing to combine. Add 1 tsp salt and 1/2 tsp black pepper and stir.
Bring the mixture to a boil, then add 2 cups dry cavatappi noodles. Reduce heat to a simmer, cover the skillet with the lid slightly ajar, and stir occasionally until the noodles are tender, about 18 minutes.
Remove the skillet from heat and stir in 1 1/2 cups diced provolone cheese slices and 1/2 cup shredded mozzarella cheese until the cheeses are melted and the sauce is smooth.
Serve the Philly cheesesteak pasta skillet warm.