In a medium pot, bring water, vinegar, sugar, salt, peppercorns and thyme to a boil. Remove from heat. Stir in onion. Let cool. Drain just before serving.
Gremolata
Combine parsley, lemon zest, garlic, olive oil and red chili flakes, and stir. Set aside.
Swiss Chard and Halibut
Preheat barbecue to high. Rub chard with 1 Tbsp (15 mL) olive oil and season to taste with salt. Grill until leaves are wilted and edges are crispy, approximately three minutes. Set aside. Rub halibut with remaining olive oil and season with salt and pepper. Grill for about five minutes on each side or just until flesh is flaky. Place fish atop Swiss chard; top with gremolata and pickled onions.
Recipe Notes
Per serving: 359 calories, 37 g protein, 15 g fat (2 g saturated fat), 18 g carbohydrates, 1 g fibre, 56 mg cholesterol, 702 mg sodium