Here's a nice and easy fish dish:

Italian Summer Opah
8 to 12oz thick Opah steaks*
1/3 cup good olive oil
4 small to 2 large ripe tomatoes, diced
3/4 cup chopped fresh basil leaves
5-8 cloves garlic, smashed and cut into large pieces
1/2 cup thin-sliced red onion
salt & pepper
large glass/ceramic casserole dish, narrow but deep**
Cut the fish into two large pieces. Lightly coat with olive oil and sprinkle with salt and pepper. Place in the bottom of the casserole dish.
Mix the vegetables and garlic. Bury the fish under them. Drizzle with around 1/4 cup olive oil. Sprinkle with salt and pepper.
Roast in a 400F oven for 25 minutes, uncovered. Dish out each piece of fish, covered in tomatoes and basil, over soft polenta, rice or risotto.
Serves 2 as a main course.***
* Swordfish steaks or tuna steaks would also work, as long as they are at least 3/4" thick.
** You want the casserole to be narrow and deep, not broad. I used a pyrex gratin dish with a 6" diameter bottom and 2" sides. The square covered corningware casseroles would probably work, or a souffle pan.
*** To serve 4, simply double the recipe and add 5 minutes to the cooking time.