Preheat oven to 350 degrees. Cut French bread in half lengthwise then scoop a shallow well in both the top and bottom halves of the bread leaving a 1" border around the edges and enough bread in the bottom of the loaf to prevent leakage. Tear or chop the bread removed from center into small pieces and set aside.

Stack the thinly sliced steaks on top of each other then slice crosswise as thinly as possible to make strips of beef. The small strips will cook quickly and be very tender.

Place a large skillet over medium-high heat then add strips of beef, salt and pepper. When beef is nearly cooked through, add onion, bell pepper and Worcestershire sauce and cook an additional 3 minutes, just to begin softening the onion and bell pepper.

Sprinkle flour over meat mixture then stir to combine. Add milk and stir to combine. Bring mixture to a boil, then reduce heat to medium-low and simmer for 2–3 minutes, stirring constantly until thickened.

Remove from heat, add shredded provolone cheese then stir until cheese has melted. Add chopped bread from center of loaf into meat mixture and stir until it has completely incorporated and the mixture is very thick. Remove from heat and season to taste with salt and pepper or a few additional dashes of Worcestershire sauce.

Transfer meat filling into the bottom half of the hollowed-out French bread, top with Swiss cheese and cover with top half of the loaf. Place on a baking sheet and bake, uncovered, for 8–10 minutes until the bread is crispy and Swiss cheese inside is melted.

Remove from oven and let sit for 5 minutes before slicing and serving.