Preheat your oven to 350°F (175°C).

In a large skillet, heat the oil over medium heat. Add the onion, green bell pepper, and mushrooms; sauté until softened. Add the garlic and cook for an additional minute.

In a large bowl, combine the ground beef, sautéed vegetables, salt, pepper, cheese whiz (if using), Worcestershire sauce, ketchup, eggs, and panko breadcrumbs. Mix until well combined.

Form the mixture into a loaf shape and place it in a greased baking dish.

Top with additional provolone slices if desired.

Bake in the preheated oven for approximately 1 hour, or until the meatloaf is cooked through and the internal temperature reaches 160°F (70°C).

Allow to rest for a few minutes before slicing and serving.