Preheat grill to medium-high or position rack in upper third of oven and preheat broiler.
Combine yogurt, scallion greens, lemon juice, cilantro, cumin, 1/4 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Set aside.
Heat oil in a large saucepan over medium heat. Add apricots, ginger, the scallion whites and 1/4 teaspoon salt. Cook, stirring, until softened, about 2 minutes. Add water and bring to a boil over high heat. Stir in couscous. Remove from heat, cover and let stand until the liquid is absorbed, about 5 minutes. Fluff with a fork.
Meanwhile, rub salmon with the remaining 1/4 teaspoon each salt and pepper. If grilling, oil the grill rack (see Tip). If broiling, coat a broiler pan with cooking spray. Grill or broil the salmon until browned and just cooked through, about 3 minutes per side. Serve with the couscous, topped with the yogurt sauce and cashews.
Ingredient note: Wild-caught salmon from the Pacific (Alaska and Washington) are more sustainably fished and have a larger, more stable population. To skin a salmon fillet, place the fillet on a clean cutting board, skin side down. Starting at the tail end, slip the blade of a long, sharp knife between the fish flesh and the skin, holding the skin down firmly with your other hand. Gently push the blade along at a 30 degrees angle, separating the fillet from the skin without cutting through either.
Kitchen tips: To toast chopped nuts, cook in a small dry skillet over medium-low heat, stirring constantly, until fragrant and lightly browned, 2 to 4 minutes.
To oil a grill rack, oil a folded paper towel, hold it with tongs and rub it over the rack. (Do not use cooking spray on a hot grill.)