Dry and season the salmon. Place salmon fillets on a paper towel–lined plate. Let sit 5–10 minutes, flip, then dry another 5–10 minutes. Season both sides with 1 tsp Kosher salt and ¼ tsp black pepper.
Roast the zucchini. Preheat oven to 375°F (190°C). Spread zucchini on a rimmed baking sheet, drizzle with 2 Tbsp olive oil, and season with ½ tsp salt and ¼ tsp pepper. Toss well, then roast 15–20 minutes, stirring once, until tender.
Prepare the couscous. Bring 1¼ cups water to a boil. Stir in 1 cup couscous, reduce to a simmer, cover, and remove from heat. Let sit 5 minutes, then fluff with a fork. Stir in remaining 2 Tbsp olive oil, roasted zucchini, and 2 Tbsp pine nuts. Toss gently to combine.
Sear the salmon. Heat 2 Tbsp oil in a large skillet over medium-high heat. Add salmon skin side down and cook 4–5 minutes, until the skin is crisp and releases easily. Flip and cook another ~3 minutes, until internal temperature reaches 110–120°F for medium-rare (it will continue cooking slightly after removal). Transfer to a plate.
Make the sauce. In the same pan, sauté 2 minced shallots for about 3 minutes, until translucent. Add 3 minced garlic cloves and 1 tsp red pepper flakes; cook 30 seconds more. Stir in 1 cup coconut milk or heavy cream and ⅓ cup mascarpone until smooth. Add ½ cup Parmesan, juice of 1–2 lemons (start with 2–3 Tbsp), 3 Tbsp chopped chives, and 3 Tbsp chopped dill. Whisk until creamy and cohesive. Taste and adjust seasoning. Remove from heat. Return salmon to the pan or spoon sauce over the top.
Serve immediately with couscous, arugula, and crusty bread.