Citrus-Marinated Halibut 2 servings This is definitely a hot-weather dish: cooked on the grill, light and clean in flavor and pretty on the plate. A quick cucumber-orange relish serves as the sauce. The fish is marinated for just 20 minutes and then grilled; any longer and the acid in the marinade will start to 'cook' the fish, ceviche style. This is also one of those dishes that you can serve to a diet-challenged audience. It's low in fat, and it's gluten-, dairy- and meat-free. Best of all, none of this was by design. It's not health food; it's just a healthful style of cooking. Halibut is used here, but any firm-fleshed fish can be substituted. The cooking method is even gentle enough for thin fillets. MAKE AHEAD: The relish and sauce for the fish can be prepared hours in advance. Ingredients For the relish 1 medium orange 1 small (4 ounces) seedless cucumber, cut into 1/4-inch dice Five to 10 mint leaves, finely chopped (1 or 2 tablespoons) 1 tablespoon apple cider vinegar 1/8 teaspoon salt 1/2 teaspoon sugar Freshly ground black pepper For the fish Juice and finely grated zest of 1 orange Juice and finely grated zest of 1 lime 1 teaspoon olive oil 1/8 teaspoon salt 2 6-ounce halibut fillets 1 medium orange, cut into thin rounds (seeds removed), for garnish Directions For the relish: Use a Microplane zester to finely grate the zest from the orange; place in a medium bowl. Cut off the top and bottom of the fruit, then stand it on a cutting board on one of the orange's cut sides. Cut away and discard the remaining peel and any white pith. Use a paring knife to cut between the sections to detach each section of fruit from its surrounding membrane, then cut the sections into 1/4-inch dice (the same size as the cucumber pieces). Squeeze any remaining juice from what's left of the orange into the bowl. Add the cucumber, mint, vinegar, salt, sugar and pepper to taste; mix well to form a relish. Let sit at room temperature, or cover and refrigerate until ready to use. For the fish: Prepare the grill for direct and indirect heat. If using a gas grill, preheat to high for 10 minutes with the lid closed. If using a charcoal grill, light the charcoal or wood briquettes; when the briquettes are ready, distribute them on one side of the cooking area. For a hot fire, you should be able to hold your hand about 6 inches above the coals for about 3 seconds. Have ready a spray water bottle for taming any flames. Brush or spray the grill grate with nonstick cooking oil spray before placing it on the grill. While the grill is heating, whisk together the orange juice and zest, lime juice and zest, oil and salt in a shallow pan large enough to hold the fish fillets. Add the fillets and turn them over to coat with the marinade. Let the fillets sit for no more than 20 minutes, turning them over after 10 minutes. While the fish marinates, place the orange slices on the grill and cover. Cook for 2 or 3 minutes until they have nice grill marks, then use a spatula to loosen and turn. Grill, covered, for 2 minutes. Transfer the slices to a plate. Use heavy-duty aluminum foil to form a small, shallow pan for the fish. Line the foil with a piece of parchment paper sprayed with nonstick cooking oil spray. Place the fish fillets in the 'pan' and discard the marinade. Turn the heat off in one section of the grill or, if using charcoal, move the fish pan to the indirect heat side of the grill. Cover and cook for about 10 minutes per inch of thickness or until the fish is done. Lay the orange slices in a semicircle on individual plates. Top each with a halibut fillet, then spoon the relish over the fish. Serve immediately. NUTRITION Per serving: 274 calories, 37 g protein, 21 g carbohydrates, 4 g fat, 1 g saturated fat, 54 mg cholesterol, 386 mg sodium, 4 g dietary fiber, 14 g sugar Recipe tested by Stephanie Witt Sedgwick; e-mail questions to food@washpost.com. 