Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Peel the sweet potato and cut it into uniform 1/2-inch cubes.
In a small bowl, toss the sweet potato cubes with 0.5 tablespoon of olive oil, the dried oregano, and half of the sea salt and black pepper.
Spread the potatoes in a single layer on the baking sheet and roast for 20-25 minutes until tender and slightly caramelized.
While the potatoes roast, pat the cod fillet completely dry with paper towels and season both sides with the remaining salt and pepper.
Heat the remaining 0.5 tablespoon of olive oil in a medium non-stick skillet over medium-high heat.
Place the cod in the skillet and sear for 3-4 minutes per side until the fish is opaque and flakes easily with a fork.
Remove the fish from the pan and set aside. In the same skillet, add the minced garlic and sauté for 30 seconds until fragrant.
Add the fresh spinach to the skillet and toss for 1-2 minutes until just wilted.
Plate the roasted sweet potatoes and sautéed spinach alongside the fish, finishing with a fresh squeeze of lemon over the cod.