Hamburger and Onion Stuffed Bread

1 large French bagette, or 6 small bagettes
1 tbsp extra-virgin olive oil
1 lb. ground beef
salt and pepper
2 medium onions, finely chopped
1 tbsp Worcestershire sauce
spicy brown mustard
4 slices cheese (Gouda, Swiss, or Mozzarella) sliced to fit bread or shredded

Preheat oven to 200. Crisp the bread then split to create boats. Hollow out bread. Switch the broiler on. Heat skillet over medium-high heat. Add EVOO and meat and season with salt and pepper. Cook 3 minutes. Add onions and cook 10 minutes more, stirring frequently. Add Worcestershire and remove from heat. Spread mustard across bottom of bread. Fill with meat mixture and top with cheese. Melt cheese under broiler.