Preheat your oven to 425°F (220°C) or set an air fryer to 400°F.
Cut the russet potato into thick wedges, toss with 0.5 tbsp of avocado oil, half of the sea salt, and half of the black pepper.
Arrange potato wedges on a parchment-lined baking sheet and roast for 20-25 minutes until the edges are golden and crisp.
While potatoes roast, pat the cod fillet dry with a paper towel and cut into 2-3 large strips.
In a small bowl, whisk together the flour, garlic powder, paprika, remaining salt, and remaining pepper.
Slowly whisk the light beer into the flour mixture until a smooth, bubbly batter forms.
Dredge the cod strips in the batter, ensuring they are fully coated, and let any excess drip off.
Lightly grease an air fryer basket or a wire rack with the remaining avocado oil and place the fish on it.
Air fry at 400°F for 10-12 minutes, flipping halfway through, until the coating is golden brown and the fish flakes easily.
Serve the crispy fish alongside the roasted potato wedges with a fresh lemon slice on the side.