I don't think I've ever had a pan-made sandwich, the way you folks across the pond make them. But I do have a deep-fill sandwich toaster and it gets a lot of use.
One of the best things I ever made in it was a cheeseburger toastie. Good quality burger, some nice white Cheshire cheese, and a rasher of smoked bacon. Just make sure the burger and bacon are pre-cooked and drained on kitchen paper first. Found that out the hard way, lol. Oh, and using garlic butter on the outside of the slices of bread, to make it crispy and golden, takes it to another level.
Blob of mayo on the plate at the side, for dipping purposes and... yum!