Line a sheet pan with foil and lightly spray the foil with cooking spray. Place salmon fillets on one side of sheet pan.
In a small bowl stir together honey and mustard, then transfer half of the mixture to another small bowl. Brush half the honey mixture on salmon fillets, then sprinkle salmon with ½ teaspoon salt and pepper.
On the other side of the sheet pan, toss asparagus with butter, garlic, and remaining ½ teaspoon salt, then spread out in an even layer.
Roast until salmon is cooked through and asparagus is tender, about 10 minutes. Salmon should reach an internal temperature of 120-125℉ for medium-rare, or 135℉ for well-done.
Right after taking the salmon out of the oven, brush it with the reserved honey mixture, using a clean brush. Serve immediately.