How to Make It
Bring a large pot of salted water to a boil. Add couscous and cook until al dente, about 10 minutes. Drain; toss with apple, parsley, arugula, onion, pine nuts, and 2 teaspoons oil in a large bowl.
Whisk mustard, lemon zest and juice, 2 tablespoons oil, and teaspoon each salt and pepper. Drizzle over couscous; toss to combine. Set aside.
Heat remaining 1 tablespoon oil in a large nonstick skillet over medium-high. Season salmon with remaining teaspoon each salt and pepper. Cook salmon, skin side down, until crispy, about 4 minutes. Flip and cook to desired doneness, 2 to 3 minutes for medium-rare. Serve with couscous salad and lemon wedges.