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.
