Preheat your oven to 425°F and line a large baking sheet with parchment paper.
Cut the Russet potato into thin wedges, toss them in a bowl with half of the avocado oil and a pinch of sea salt, then spread them in a single layer on the baking sheet.
Roast the potato wedges for 10 minutes while you prepare the fish.
In a shallow bowl, whisk together the flour, light beer, garlic powder, and paprika until a smooth, thick batter forms.
Pat the cod fillet completely dry with paper towels and season both sides with the remaining sea salt and black pepper.
Dip the cod into the batter, ensuring it is fully coated, and place it on the baking sheet next to the potatoes.
Lightly brush or spray the top of the battered fish with the remaining avocado oil to encourage browning.
Bake everything for an additional 12-15 minutes, flipping the potatoes halfway through, until the fish is opaque and the coating is crispy and golden.