Preheat your oven to 400°F and line a baking sheet with parchment paper.
Halve the baby potatoes and toss them on the baking sheet with half of the avocado oil, half of the sea salt, and the garlic powder.
Roast the potatoes for 20 minutes, then move them to one side of the pan and add the trimmed asparagus; roast both for another 10 minutes.
While vegetables roast, pat the cod fillets completely dry with paper towels and season both sides with the remaining sea salt and black pepper.
Heat a cast-iron skillet over medium-high heat with the remaining avocado oil.
Place the cod in the hot skillet and sear for 3-4 minutes per side until a golden-brown crust forms and the fish flakes easily.
In a small mixing bowl, whisk together the Greek yogurt, finely chopped fresh dill, and lemon juice until smooth.
Plate the golden cod alongside the roasted potatoes and asparagus, then drizzle the lemon-dill sauce over the fish before serving.