Light and flaky, halibut is an ideal choice for a simple summer dinner. Here halibut steaks are marinated in a watermelon-raspberry vinaigrette, quickly grilled, and then topped with refreshingly tart watermelon salsa. Don't be fooled: This fresh and exciting entrée is ready to serve in minutes.
Using a fork, mash 1 cup of the watermelon in a wide, shallow dish until all of the juices are released. Stir in 1 tablespoon of the vinegar and oil, and season with salt and pepper, to taste, to make a marinade. Add the halibut, turn to coat, cover, and refrigerate for 2 hours.
In a bowl, toss together the remaining watermelon, remaining vinegar, scallion, and cayenne. Season with salt and pepper, to taste, to make a salsa. Set aside.
Preheat a gas grill or cast-iron grill pan on moderate heat.
Grill the halibut until cooked through, about 4-5 minutes per side, depending on the thickness. Transfer the fish to a serving platter and top with the salsa. Serve immediately.