Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easy cleanup.
In a small bowl, whisk together the olive oil, minced garlic, dried thyme, dried rosemary, salt, and pepper.
Place the trimmed asparagus on one side of the prepared baking sheet. Drizzle half of the oil mixture over the asparagus and toss to coat evenly. Spread the asparagus into a single layer.
Place the cod fillets on the other side of the baking sheet. Brush the remaining oil mixture evenly over the top of the cod fillets.
Arrange the thin lemon slices over the top of each 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-crisp. Cooking time depends on the thickness of your fish.
Remove from the oven. Sprinkle the fresh chopped parsley over the fish and vegetables before serving.
Notes
For a different flavor, substitute fresh dill for the rosemary and thyme to make Lemon Dill Cod.
If your asparagus spears are very thick, toss them with the oil mixture and roast them alone for 5 minutes before adding the cod to the pan.
You can substitute halibut or tilapia for the cod. Adjust cooking time as needed.