When I do those i always add cheese, peppers onions a little au jus and then bake them at broil for a minute or two.
Made Philly Steak sandwiches Friday/Saturday. I toasted the bun under the broiler ’til just starting to brown, then spooned on some au jus and added the steak, veggies and cheese and broiled it again until the cheese was bubbly. Much better with the crunch. Thanks Bearcat!!