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 them on one side of the sheet pan.
Pat the cod fillet dry with a paper towel and place it on the other side of the pan.
In a small bowl, whisk together the olive oil, minced garlic, dried oregano, sea salt, and black pepper.
Drizzle the herb oil over both the cod and the asparagus, tossing the asparagus to coat evenly.
Slice the half lemon into thin rounds and lay them across the top of the cod fillet.
Bake for 12-15 minutes, or until the cod is opaque and flakes easily with a fork and the asparagus is tender-crisp.
Warm the pre-cooked quinoa and place it in a serving bowl.
Top the quinoa with the baked cod and asparagus, then garnish with freshly chopped parsley before serving.