Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
In a small mixing bowl, whisk together the olive oil, the juice from the lemon half, minced garlic, dried oregano, sea salt, and black pepper.
Trim the woody ends off the asparagus spears and place them on one side of the prepared baking sheet.
Place the cod fillet on the other side of the baking sheet.
Drizzle the lemon-herb marinade over both the cod and the asparagus, using a brush or your hands to ensure the asparagus is evenly coated.
Bake in the center of the oven for 12 to 15 minutes, or until the cod is opaque and flakes easily with a fork and the asparagus is tender-crisp.
While the fish bakes, warm your pre-cooked quinoa in a small saucepan or microwave.
Plate the cod and roasted asparagus over the bed of warm quinoa, garnishing with finely chopped fresh parsley before serving.