Preheat oven to 400 degrees F. Line a baking sheet with parchment paper or spray with nonstick cooking spray; set aside.

Melt butter in a saucepan over medium-high heat. Add garlic and sauté for 1 minute. Whisk in flour and cook for an additional minute. Slowly whisk in milk and season with salt, pepper and nutmeg. Let simmer for a few minutes until thickened then remove from heat and set aside.

Cut french bread in half lengthwise and place cut side up on baking sheet; set aside.

Heat olive oil in a large skillet over medium-high heat. Season flank steak with salt and pepper, then cook for 1-2 minutes, stirring occasionally. Toss steak in Worcestershire sauce, then remove from skillet and set aside on a plate.

Add bell pepper, onion and mushrooms to the same skillet and cook for 2-3 minutes, or until vegetables are tender then remove from heat.

Divide and spread prepared sauce evenly between the two loaves of french bread. Top each half of bread with half the cheese, steak and vegetables. Cook for 10-12 minutes, or until cheese is melted and golden brown. Cut into slices and serve.