Preheat your oven to 425°F and line a large baking sheet with parchment paper.
Slice the russet potato into even wedges and toss them in a bowl with 0.5 tablespoons of avocado oil and a pinch of sea salt.
Spread the potato wedges on the baking sheet and roast for 25 to 30 minutes, flipping once, until they are crispy and golden on the outside.
Pat the cod fillets very dry with paper towels to ensure the batter sticks, then season both sides with sea salt and black pepper.
In a shallow dish, whisk together the arrowroot powder, garlic powder, and paprika, then slowly pour in the light beer while whisking until a smooth batter forms.
Heat the remaining 0.5 tablespoons of avocado oil in a large non-stick skillet over medium-high heat.
Dredge each piece of cod into the beer batter until fully coated, allowing any excess to drip off before carefully placing it into the hot skillet.
Cook the fish for 3 to 4 minutes per side until the crust is deeply golden and the fish flakes easily with a fork.
Remove the fish from the pan and serve immediately alongside the hot roasted potato wedges.