Method:
Preheat oven to 400°F. Place grapes and fennel or onion in a roasting pan, drizzle with olive oil and sprinkle with ¼ teaspoon of the salt and ¼ teaspoon of the pepper. Roast until grapes just begin to shrivel and fennel or onion just begins to brown, about 25 minutes, stirring once halfway through cooking.
Sprinkle salmon with remaining ¼ teaspoon salt and ¼ teaspoon pepper. Stir grape mixture again and arrange salmon, skin side down, on top. Continue roasting until salmon is just cooked through, 10 to 12 more minutes. Transfer fish to a platter or plates. Toss grape mixture with parsley and serve along with salmon.