In a large skillet, drizzle some olive oil and heat over medium-high.
Add the sliced onions and bell peppers to the skillet. Sauté for about 3-5 minutes until they become tender. If using, add mushrooms and continue to cook for an additional 3 minutes.
Push the vegetables to the side of the skillet and add the ground beef. Break it apart and cook until it is no longer pink, which should take about 5-7 minutes.
Stir in the garlic powder, Worcestershire sauce, salt, and pepper. Mix everything together thoroughly for about 2 minutes.
Lower the heat to low. Place a slice of cheese over the beef mixture. Cover the skillet with a lid and let the cheese melt, which will take about 2-3 minutes.
While the cheese is melting, slice the hoagie rolls lengthwise without cutting all the way through.
Once the cheese has melted, spoon the beef and vegetable mixture into each roll.
Optionally, toast the rolls for added texture before serving. Enjoy your delicious Ground Beef Philly Cheesesteaks filled with rich flavors and satisfying textures!