Heat olive oil in a skillet over medium heat. Add the chopped onions, bell peppers, and garlic. Cook until the vegetables are softened, about 5-7 minutes. Remove from heat and let cool.
In a large mixing bowl, combine the ground beef, breadcrumbs, shredded cheddar cheese, shredded provolone cheese, milk, egg, Worcestershire sauce, salt, pepper, and the cooked vegetables. Mix until everything is well combined.
Spray a loaf pan with cooking spray. Transfer the meatloaf mixture into the pan and shape it into a loaf.
Bake in the preheated oven for about 45-50 minutes, or until the meatloaf is cooked through and browned on top.
Remove the meatloaf from the oven and let it rest for a few minutes before slicing.
Serve slices of the Philly Cheesesteak Meatloaf with your favorite sides, such as roasted vegetables or a side salad.