Preheat your oven to 425°F and line a baking sheet with parchment paper.
Slice the russet potato into half-inch thick wedges and pat them very dry with a paper towel to ensure crispness.
Toss the potato wedges with 0.5 tablespoons of olive oil and a pinch of salt and pepper, then roast for 25 minutes until golden brown.
While potatoes roast, pat the cod fillet dry with paper towels and season both sides with the remaining salt and pepper.
Dredge the seasoned cod in arrowroot powder, shaking off any excess to create a light and clean coating.
Heat the remaining 0.5 tablespoons of olive oil in a non-stick skillet over medium-high heat.
Sear the cod for 3 to 4 minutes per side until the crust is golden and the fish flakes easily with a fork.
Steam the frozen peas in a small saucepan with a tablespoon of water for 3 minutes until bright green.
Plate the crispy cod with the potato wedges and peas, finishing the dish with a bright squeeze of fresh lemon.