Chances are, unless you've been to Hawaii, you are unfamiliar with the Ono fish. It is also known as Wahoo on the island, and aside from there you can sometimes find it along the West Coast. I happened across in the frozen fish area at my local Trader Joe's and it was remarkably affordable AND very recently caught and packed. Anyway it is a dense, white fish and is similar enough to both Halibut and Mahimahi - so you can substitute those two fishes if Ono is just out of reach.
Anyway, the only way to prepare this is on the grill, which means that a marinade is in order. I used a simple marinade that just included 1/4 cup soy sauce, 1/4 cup white wine, two teaspoons of sesame oil, 1 minced clove of garlic (more if you like garlic...we used close to two cloves) and about 1 tbsp of chopped, fresh ginger. I let it soak, covered in the fridge for close to two hours (you can let it sit for more but I wouldn't exactly do it a day ahead of time or anything as if it was beef) then took it to the grill.
As it is a lean fish (no fat to trim!) you want to avoid overcooking, so do it over a medium flame. For timing figure something like six to eight minutes per inch of thickness of the filet - ours worked out to be closer to eight minutes a side but we kept a close watch!!!
To accompany the fish, I sautéed fresh spinach (stems and all) with a little olive oil, a few splashes of dry white wine and ground white pepper. Then I topped that with the garlic cloves I had roasted in the oven in more olive oil, savory and pink Himalayan salt (about 10-15 minutes, small ramekin, on 350 degrees).
Also served with a sticky brown jasmine rice.