Preheat the oven to 400 degrees F.
Coat a shallow baking dish with cooking spray. Season both sides of salmon with salt and pepper. Place salmon in prepared baking dish.
In a medium bowl, whisk together the Dijon, honey, water, lemon juice, mustard powder, and garlic powder. Remove 1/2 cup of the mustard sauce and set aside. Pour the remaining sauce over the salmon fillets in the pan. Roast the salmon, uncovered, until fork tender, about 15 minutes.
Stir the dill into the reserved mustard sauce. Serve 1/3 of the roasted salmon (4 fillets, each about 4 ounces after cooking) with the dill-spiked mustard sauce spooned over the top. Refrigerate the remaining salmon up to 3 days or freeze for up to 3 months; thaw it completely in the refrigerator or microwave for 3 to 5 minutes on LOW before using.