Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Wash and peel the sweet potato, then dice it into uniform 1/2-inch cubes to ensure even roasting.
Place the sweet potato cubes on the baking sheet and toss with 0.5 tablespoon of olive oil, half of the sea salt, and all of the garlic powder.
Spread the potatoes in a single layer and roast in the oven for 15 minutes.
While the potatoes roast, snap off the woody ends of the asparagus and pat the cod fillet dry with a paper towel.
Remove the baking sheet from the oven and slide the sweet potatoes to one side to make room for the fish and vegetables.
Place the cod fillet and asparagus spears on the empty side of the pan.
Drizzle the remaining 0.5 tablespoon of olive oil over the fish and asparagus, then season everything with the remaining salt, black pepper, and dried oregano.
Return the pan to the oven and bake for an additional 10 to 12 minutes, or until the fish is opaque and flakes easily with a fork.
Remove from the oven and immediately squeeze the fresh lemon juice over the fish and asparagus before serving.