1. Over a bowl, peel and section grapefruit to measure 1 1/2 cups sections; squeeze membranes to extract 1/2 cup juice. Set juice aside. Combine grapefruit sections, fennel, and parsley in a medium bowl. Add 2 teaspoons oil and 1/4 teaspoon kosher salt; toss gently to combine. Heat remaining 1 teaspoon oil in a large nonstick skillet over medium-high heat. Sprinkle scallops with 1/4 teaspoon kosher salt and 1/4 teaspoon freshly ground black pepper. Add scallops to pan; cook for 2 minutes on each side or until desired degree of doneness. Remove scallops from pan; keep warm. Add reserved 1/2 cup juice to pan; cook until reduced to 1/4 cup (about 2 minutes). Remove from heat. Place 1 cup fennel mixture on each of 4 plates. Divide scallops evenly among plates; top each serving with 1 tablespoon reduced juice.