Here's one of my very favorite one-dish meals. It's a whole, baked sea bass recipe James Peterson's Fish & Shellfish. To paraphrase:
1/2 cup evoo
2 large Idaho potatoes, peeled and cut into 1/8-inch-thick slices
2 garlic cloves finely chopped
1/2 teaspoon chopped fresh thyme
s&p
3 tomatoes, peeld, seed, and coarsely chopped
15 brine-cured black olives, pitted and coarsely chopped
Preheat oven to 450. Brush baking dish with oil. Overlap half the potatoes and sprinkle with half the garlic, thyme, s&p and evoo. Add remaining potatoes and sprinkle with the rest of the g, t, s&p, and evoo. Bake potatoes for 29 minutes. Season fish with evoo, s&p and place on potatoes. Add tomatoes & olives around the fish. I bake the whole fish about an additional 30 minutes.
I nearly always do this with a whole fish, but the recipe can easily be adapted for fillets. This same recipe is good with a large variety of fish; I've used blackfish, snapper, and striped bass all with excellent results.