While your grill is preheating to medium-high heat, trim the asparagus ends (about 2 inches from the bottom) and pat the salmon fillet dry with paper towels to help develop a better sear and prevent sticking.

In a small bowl, combine salt, black pepper, and dried oregano. Brush the olive oil evenly over both the salmon skin and the asparagus spears, then season generously with the herb mixture on all sides.

Place the salmon skin-side up on the grill grates, arranging the lemon slices directly beside it. Lay the asparagus spears perpendicular to the grill grates.

Grill for 6-8 minutes without moving the salmon, then flip the salmon flesh-side down and rotate or flip the asparagus. Continue cooking for 5-6 minutes until the salmon is opaque and flakes easily with a fork, and the asparagus is tender with light char marks.

While the salmon and asparagus are finishing, melt the butter in a small saucepan over low heat or a heat-safe bowl near the grill.

Once melted, stir in the lemon zest, fresh lemon juice, and garlic powder until well combined, keeping the sauce warm.

Transfer the grilled salmon and asparagus to a serving platter or individual plates. Discard the grilled lemon slices or use them as a garnish if desired.

Pour the warm lemon-butter sauce evenly over the salmon and asparagus, then finish with freshly chopped parsley scattered on top.