Preheat oven to 400 degrees.

In a skillet over medium high heat, add vegetable oil and beef. Let sit for 2 minutes to develop a crust on the beef, then break apart with spatula. Cook for 3-4 minutes, or until halfway cooked through.

Add onions and peppers to the skillet and sauté for 4-5 more minutes, or until beef is cooked through and vegetables are tender. Drain off any extra liquid/fat.

Add Worcestershire sauce, ketchup, brown sugar, salt, and pepper to skillet and mix well to combine. Bring to a quick boil, then reduce heat and simmer, covered, for about 5 minutes; stirring occasionally. Remove from heat and add half of the mozzarella cheese; stir until melted through.

Place half of the loaf of bread on a baking sheet. Take out some of the bread from the center of the loaf making a SMALL indentation (see video). Spoon sloppy joe mixture on top of bread, spreading evenly. Add remaining ½ cup mozzarella cheese over the top evenly. 

Cover loosely with foil and place into oven. Bake covered for 10 minutes; remove foil. Turn oven to broil, and cook 2-3 minutes or until cheese is bubbling and lightly browned. Watch carefully as it can burn quickly. 

Remove from oven, let sit 5 minutes. Using a large knife, cut into slices and serve immediately.