Prep the fish and miso-butter: Pat each sea bass fillet dry with paper towels (dry fish gives the best sear). Season both sides lightly with sea salt and a pinch of white pepper. In a small bowl, mash the white miso with the unsalted butter until smooth and homogenous — this creates a glossy, savory glaze that melts onto the hot fish and adds umami without overpowering the delicate flesh.

Prepare the vegetables while the pan heats: Spiralize the zucchinis and place the noodles in a colander. Toss the zucchini with 1 tsp rice vinegar and a pinch of salt to macerate briefly (1–2 minutes) — the acid wakes up the vegetable’s flavor and draws out a little moisture so the noodles don’t get watery when finished. Trim bok choy bases, halve lengthwise if large, and rinse thoroughly to remove grit.

Quick-steam the baby bok choy: Bring a wide skillet or shallow pot with 2–3 cm (1 inch) of water to a vigorous simmer. Add the bok choy cut-side down, cover, and steam for 2–3 minutes until stems are just tender but leaves remain bright green — quick steaming preserves crunch and color. Immediately transfer to a bowl and season with a light pinch of salt; the hot bok choy will continue to carry heat while you finish the fish and noodles.

Sear the sea bass (skin side first) for a crisp skin and even cook: Heat a large nonstick or stainless-steel skillet over medium-high heat until shimmering. Add 1 tbsp neutral oil (this has a high smoke point), then place the fillets skin-side down and press gently for 10 seconds to prevent curling — contact with the hot pan renders fat and yields a crisp skin. Cook skin-side down without moving for 3–4 minutes until the skin is golden brown and the fish releases easily.

Finish the fillets and glaze: Flip the fillets and reduce heat to medium. Add a dollop (about 1 tbsp per fillet) of the miso-butter to the pan beside the fish so it melts quickly. Spoon the melted miso-butter over the top of the fish as it finishes cooking for 1–2 minutes — basting both cooks the top gently and deposits the glaze for a lacquered finish. Cook until the fish is opaque and flakes easily with a fork (total cook time ~5–6 minutes depending on thickness).

Dress and warm the zucchini noodles: While the fish rests for 1–2 minutes after cooking, wipe out the skillet and return to medium heat. Add the spiralized zucchini and toss briefly for 30–45 seconds — you want to warm and slightly soften them but not sweat them until soggy. Finish with the toasted sesame oil, the remaining 1 tsp rice vinegar if desired to taste, and most of the sliced spring onion (reserve a few slices for garnish). Toss to coat; the sesame oil provides nutty aroma while the short cook prevents waterlogging.

Plate with attention to texture and temperature: Pile a nest of sesame zucchini noodles on each plate, lay a miso-butter glazed sea bass fillet on top (skin-side up for contrast), and arrange 2 steamed baby bok choy heads alongside. Spoon any leftover pan glaze over the fish and sprinkle with toasted sesame seeds and the reserved spring onion slices for brightness and crunch. A final pinch of white pepper on the fish enhances aroma without adding visible flecks.

Serve immediately: This dish is best served hot so the miso-butter is glossy and the zucchini retains a little snap. If you must hold it briefly, keep the plated fish and noodles in a warm (not hot) oven at 90–100°C (200–210°F) for up to 5 minutes while you finish sides.