My favorite is to crush some garlic, rub it all over and inside the cavity (leaving some little traces of the crushed pieces, then sprinkle with just a little origano, salt and black pepper, drizzle with olive oil, and put on a piece of oiled parchment paper on an oven sheet (low sides not to create steam) in a very very hot oven, with some potatoes around it, Very simple and very good.
As soon as the trout is cooked, remove and keep cooking the potatoes till they color and get nice and crispy.