Heat the oven to 375°F. Boil cavatappi in water with the tablespoon salt until 3 minutes short of the package time and drain.
Heat 2 teaspoons oil in a wide skillet and cook onion and pepper for 8 to 10 minutes until softened and lightly browned. Transfer to a bowl.
Add remaining oil and sear steak in 2 batches for 2 to 3 minutes each until at least 145°F. Season with 1/4 teaspoon salt and pepper and rest for 3 minutes; drain excess juices.
Melt butter in a saucepan and whisk in flour for 1 minute. Gradually whisk in milk and broth and simmer for 3 minutes, then remove from heat and stir in 6 oz provolone, Worcestershire and remaining salt.
Fold pasta, vegetables and steak into the sauce and transfer to a deep 9-by-13-inch baking dish. Scatter with remaining provolone, cover with foil and bake for 20 minutes.
Uncover for 5 to 8 minutes until the center reaches 165°F and the surface is lightly browned. Rest for 5 minutes before serving.