Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Trim the woody ends off the asparagus and place the spears on one side of the prepared sheet pan.
In a small bowl, whisk together the olive oil, the juice of half the lemon, minced garlic, dried oregano, sea salt, and black pepper.
Place the cod fillet on the other side of the sheet pan and drizzle the herb marinade over both the fish and the asparagus, tossing the asparagus to coat evenly.
Slice the remaining half of the lemon into thin rounds and place them on top of the cod fillet.
Bake for 12 to 15 minutes, or until the cod is opaque and flakes easily with a fork and the asparagus is tender.
Serve the baked cod and asparagus over a bed of warm cooked quinoa to soak up the flavorful juices.