Friend is looking for a pan to put in his outdoor grill. To cook fish.
Cast iron skillet is too heavy and you have to treat it. Do you think a
Simple oven pan might work. Or would that melt on the hot charcoals

Disposable aluminum pans work well.

By oven pan do you mean broiler pan, the kind that come with an oven?
That's OK.
Some use tinfoil as a disposable pan, or line the oven pan with foil.

Some wrap fish completely in foil or corn husks for a more delicate poached effect.

But you miss the taste you get only from the fire. Plenty of people grill fish right on the open rack. It isn't messy if the rack is well oiled. Supposedly! I've never done it. But certain fish from my childhood like trout I would want fried in a cast iron skillet, with a bit of cornmeal. Yum

Thanks