Season the salmon with paprika, cumin, salt, pepper, cayenne, and olive oil. Toss to coat and let sit while preparing the couscous.
Heat the olive oil in a medium saucepan over medium heat. Add the onion and cook until soft and translucent, 6 to 8 minutes. Stir in the couscous, water, and salt. Bring to a boil, cover, reduce heat to low, and simmer until the liquid is absorbed and the couscous is tender, 10 to 12 minutes. Remove from the heat, fluff with a fork, and fold in the parsley.
Thread the salmon onto skewers, alternating with folded lemon or orange slices if using.
Heat a grill pan or large skillet over medium heat and lightly coat with olive oil. Cook the skewers, turning occasionally, until lightly charred and just cooked through, 8 to 10 minutes total.
Meanwhile, whisk together the olive oil, lemon juice, parsley, cilantro, mint, garlic, honey, salt, and pepper until smooth and glossy.
Spread the couscous onto a serving platter and arrange the salmon skewers over the top. Spoon over the lemon herb sauce and serve immediately.