Combine the vinegar, soy sauce, ginger, garlic, wasabi (or horseradish), and sugar in a mixing bowl or blender.

Marinate the fish in the sauce for 15 to 30 minutes. (While marinating, place in the refrigerator.)

Preheat the oven to 400 degrees Fahrenheit.

Coat an oven-safe pan or casserole dish with oil.

Brush the marinade off the fish with your fingers and place it in the prepared pan. Set aside marinade.

Insert the pan into the oven.

Cook for 8 minutes per 1" thickness of fish, or until opaque and easily pierced with a fork. (Thinner fish will cook faster, so pay attention to the thickness of your fillets.)

Cook the fish without flipping it halfway through.

Pour the marinade into a small pot while the fish cooks.

Heat over medium heat until it comes to a boil, then reduce to a low heat for 2-3 minutes. Remove the pan from the heat and cover it to keep the sauce warm.

When the yellowtail is done, remove it from the oven and brush it with the teriyaki sauce. Serve the remaining sauce on the side or drizzled over side dishes (like rice or vegetables.)

Serve the fish right away.