Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Trim the tough, woody ends off the asparagus spears and place them on one side of the prepared baking sheet.
Pat the salmon fillet dry with a paper towel to ensure a better sear and place it on the other side of the sheet.
In a small glass bowl, whisk together the extra virgin olive oil, fresh lemon juice, dried oregano, garlic powder, sea salt, and black pepper.
Drizzle the herb and oil mixture evenly over both the salmon fillet and the asparagus spears, using your hands or a brush to coat thoroughly.
Place the fresh lemon slice on top of the salmon fillet to infuse it with bright citrus notes during the roasting process.
Roast in the center of the oven for 12 to 15 minutes, or until the salmon is opaque and flakes easily with a fork and the asparagus is tender.