Pat the salmon fillets dry with a kitchen towel, then season generously with salt and pepper on both sides.
Toss the asparagus spears with olive oil, lemon zest, and a pinch of salt, ensuring they’re evenly coated.
Preheat the grill to high heat until it’s hot and slightly smoky, then clean the grates with a towel lightly coated in oil to prevent sticking.
Place the salmon fillets skin-side down on the hot grill, pressing gently to ensure contact and prevent curling. Grill for about 3-4 minutes until the skin is crispy and golden, then flip carefully with tongs.
Reduce the heat slightly and continue grilling the salmon for another 4-5 minutes, until the flesh feels firm and flakes easily when tested with a fork.
Meanwhile, place the asparagus on the grill, laying them across the grates for even charring. Grill for 3-4 minutes, turning occasionally, until they develop dark grill marks and a smoky aroma.
Remove the salmon and asparagus from the grill; let the salmon rest for a minute, then serve with the charred asparagus on the side, finished with a squeeze of fresh lemon juice.