Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Prepare the asparagus by snapping off the woody bottom ends and spreading the spears out on one side of the prepared baking sheet.
Pat the cod fillets dry with a paper towel to ensure a better texture and place them on the other side of the baking sheet.
In a small bowl, whisk together the extra virgin olive oil, the juice of half the lemon, minced garlic, dried oregano, sea salt, and black pepper.
Drizzle the lemon-herb marinade evenly over both the cod fillets and the asparagus spears, using a brush or your hands to coat them thoroughly.
Slice the remaining half of the lemon into thin rounds and place them on top of the cod fillets.
Bake for 12 to 15 minutes, or until the cod is opaque and flakes easily with a fork and the asparagus is tender and slightly charred.
Serve immediately, drizzling any remaining pan juices over the fish for extra flavor.