1. Preheat oven to 400ºF. Warm 1 Tbsp. olive oil in a small saucepan over medium heat. Add shallot and cook, stirring, until softened, about 3 minutes. Stir in couscous, orange zest, 1 1/2 cups water and 1/2 tsp. salt and bring to a boil. Cover, remove from heat, and let stand for 5 minutes. Fluff with a fork, stir in cranberries and pistachios, and season with more salt, if desired.
2. Mist 4 large sheets of heavy-duty aluminum foil with cooking spray. Mound some couscous in middle of each sheet. Top each with a salmon fillet. Drizzle with remaining oil and sprinkle with salt. Fold edges of packets together tightly on top to seal.
3. Place packets on a baking sheet and bake until salmon is cooked through, about 15 minutes. Carefully unfold packets to release steam, then serve.