Make the miso-citrus glaze: In a small bowl whisk together the white miso, mirin, low-sodium soy sauce, honey (or maple), and finely grated orange zest until smooth. This combination balances savory (miso), sweet (honey/mirin), salty (soy), and bright citrus — the result is a glossy glaze that will caramelize briefly when finished on the fish.

Marinate the fish briefly: Pat the Arctic char fillets very dry with paper towel (dry skin crisps best). Lightly brush both sides of the fillets with about half of the glaze, reserve the rest for finishing. Marinate at room temperature for 10–15 minutes (short marination prevents the miso from over-salting or 'cooking' the fish the way longer acidic marinades do).

Parboil the fingerlings for even, fast roasting: Put the halved fingerling potatoes in a pot, cover with cold salted water, bring to a simmer and cook until just tender — about 8–10 minutes depending on size. Parboiling softens the interior and shortens pan-roasting time so the exterior crisps quickly without overcooking the fish or veggies.

Dry and score the potato surfaces: Drain the potatoes well and let them steam dry in the colander for a minute. Shake them to rough up the surface a bit — extra surface texture helps them crisp in the pan. Season lightly with salt and pepper.

Pan-roast the potatoes: Heat a large heavy skillet (cast-iron or stainless steel) over medium-high heat until hot. Add 2 tablespoons olive oil and swirl. Place potatoes cut-side down in a single layer and press gently. Let them cook undisturbed until golden-brown and crisp, about 6–8 minutes. Flip and brown the other side 2–3 minutes. Browning creates Maillard flavor — the caramelized bits give the dish a toasty counterpoint to the miso glaze.

Keep the potatoes warm: Transfer the crisped potatoes to a warm plate and cover loosely with foil or place in a low oven (90–100°C / 200°F). This keeps them crisp while you cook the fish and peas.

Prepare the snap pea stir-fry base: In a bowl toss the sugar snap peas with the minced garlic, sliced spring onions, 1 teaspoon mirin (from reserved or extra if you like), and a pinch of salt. This readies the peas for a quick high-heat stir so they keep a bright color and firm-crisp bite.

Sear the fish — technique for crisp skin: Wipe the skillet used for potatoes if necessary and return to medium-high heat. Add a little neutral oil if the pan is dry. Season the fish skin lightly with salt (not too much — miso is already salty). Place the fillets skin-side down and press with a spatula for 10–15 seconds to ensure even contact — this prevents the skin from shrinking and curling. Cook skin-side down until the skin is deeply golden and crisp and the fish is about two-thirds cooked through (for 160 g fillets, about 4–5 minutes depending on thickness). Searing the skin first renders fat and gives you the signature crunch.

Finish the fish gently: Flip the fillets and reduce heat to medium-low. Brush the flesh side with the remaining miso-citrus glaze and cook 30–60 seconds more — just long enough for the glaze to warm and begin to gloss but not burn. Sugar in the glaze caramelizes quickly; low heat prevents bitter char while still building sticky shine.

Quickly stir-fry the sugar snap peas: While the fish finishes, heat a separate small skillet over high heat. Add the toasted sesame oil and the garlic-spring onion-pea mixture and toss constantly for 60–90 seconds until the peas are vibrant green and slightly blistered. Add 1 teaspoon low-sodium soy sauce and 1/2 teaspoon honey (or a splash more mirin) to balance the heat and finish with toasted sesame seeds. High heat and short cook time preserve snap and color.

Plate and finish: Arrange a bed of crispy fingerling potatoes on each plate, nestle a fillet skin‑side up (to showcase the crisp skin), spoon the sesame sugar-snap peas alongside, and sprinkle the dish with chopped cilantro or chives and an extra pinch of toasted sesame seeds. A light drizzle of any pan juices or a few drops of lemon or yuzu juice brightens the plate if desired.

Rest a moment and serve: Let the fish rest 1 minute before serving so juices redistribute. The combination of textures — crisp skin, tender flesh, crunchy peas and roasted potatoes — should be warm, balanced, and aromatic.