Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Trim the woody ends off the asparagus spears and place them on one side of the prepared sheet pan.
Place the salmon fillet on the other side of the pan, skin-side down.
In a small bowl, whisk together the olive oil, minced garlic, dried oregano, sea salt, and black pepper.
Drizzle the herb oil mixture over both the salmon and the asparagus, using your hands or a brush to ensure the asparagus is evenly coated.
Slice half of the lemon into thin rounds and arrange them directly on top of the salmon fillet.
Roast in the center of the oven for 12-15 minutes, or until the salmon flakes easily with a fork and the asparagus is tender-crisp.
Squeeze the juice from the remaining lemon over the entire pan before serving warm.