Move the oven rack to the second-highest position and preheat the broiler.

Line a baking sheet with foil and set aside.

Cut the submarine rolls almost all the way in half. Use your fingers to spread the rolls open. Brush the inside and outside of the rolls with melted butter and place the rolls on the prepared baking sheet.

Place the rolls under the broiler and let them toast until the edges are golden brown about 1-3 minutes. Watch the rolls constantly because they can burn in a blink of an eye!

Remove the rolls from the oven and let them cool.

Preheat a large skillet over medium-high heat. Add oil, swirl it around the pan and add ground beef. Using the back of a wooden spoon break up ground beef and cook until browned, about 5-6 minutes.

Add bell pepper and onion and cook, stirring occasionally, until tender; 3-4 minutes.

Add Worcestershire sauce and beef stock. Bring mixture to bubble and continue to cook until almost all liquid evaporates; 3-4 minutes. Season the mixture with salt and pepper to taste.

Add the torn cheese pieces to the filling and stir it to combine. Continue to cook until the cheese is nice and melted.

Add 1/6 of the meat mixture to a toasted roll. Repeat with remaining rolls and serve!