Preheat oven to 350°F. In a baking dish, toss together grapes, vinegar, oil, basil, garlic, onion, salt and pepper. Roast in preheated oven for 20 minutes, stir, and roast for another 15 minutes.

When grapes are almost done, heat 2 tablespoons oil in a large, non-stick skillet. Pat fish dry and season both sides with salt and pepper. Add to skillet and cook until opaque and flaky - about 3 minutes per side.

To serve, top each fillet with some of the roasted grape mixture, drizzling on the pan juices. Garnish with some fresh basil.