Preheat your grill or a cast-iron grill pan to medium-high heat.
Pat the salmon fillet dry with a paper towel to ensure a clean sear.
In a small bowl, whisk together the olive oil, finely chopped parsley, dill, garlic powder, and the juice from the half lemon.
Brush the herb marinade evenly over the salmon fillet and the trimmed asparagus spears.
Season both the salmon and the asparagus with the sea salt and black pepper.
Place the salmon on the grill skin-side down and cook for 4 to 5 minutes without moving it.
Add the asparagus spears to the grill alongside the salmon.
Carefully flip the salmon and grill for an additional 3 to 4 minutes until the internal temperature reaches 145°F and it flakes easily.
Continue grilling the asparagus for 5 to 6 minutes total, turning occasionally until tender and lightly charred.
Remove from heat and serve the salmon alongside the asparagus with an extra squeeze of fresh lemon.