Preheat and Prepare: Preheat your oven to 425°F (220°C). Line a large baking sheet with parchment paper for easy cleanup.
Make the Glaze: In a small mixing bowl, combine the honey, Dijon mustard, whole grain mustard, lemon zest, garlic powder, and kosher salt. Whisk until smooth and set aside.
Roast Vegetables: Spread the peeled and chopped carrots and the sliced onions evenly on the prepared baking sheet. Pour about half of the honey dijon glaze over the vegetables. Use your hands to toss them until well-coated. Roast in the preheated oven for 15-20 minutes, or until they begin to soften and caramelize.
Cook the Couscous: While the vegetables are roasting, cook the pearled couscous according to the package instructions. Feel free to add additional spices like garlic powder, turmeric, or paprika for extra flavor.
Roast Salmon: Remove the baking sheet from the oven and use a spatula to create space in the center for the salmon fillets. Place the salmon fillets on the baking sheet and brush them with the remaining honey dijon glaze. Return the baking sheet to the oven and roast for an additional 12-15 minutes, or until the salmon is cooked to your desired doneness.
Serve: Plate the cooked couscous, then top with the roasted salmon, carrots, and onions. Drizzle with any remaining glaze or a bit of extra honey if desired, and garnish with fresh parsley.