Make the miso glaze: in a small bowl whisk together the white miso paste, mirin and honey with half the grated ginger (about 1/2 inch) and half the minced garlic. Add 1 tsp sesame oil and 1 tsp warm water if needed to make a brushable, glossy glaze. (Why: combining the mirin and honey balances miso’s saltiness with sweetness; thinning slightly makes it easier to glaze the fish evenly.)

Pat the cod fillets dry and season very lightly with salt and a few grinds of black pepper. Place the fillets on a plate and brush both sides with half of the miso glaze. Let rest at room temperature for 8–10 minutes. (Why: drying the surface helps the glaze stick and caramelize; a short rest lets the miso slightly penetrate the surface without over-salting the delicate fish.)

Preheat the oven to 220°C / 425°F with the top rack about 12–15 cm (5–6 in) from the broiler element. Bring a large pot of salted water to a rolling boil for the soba noodles. (Why: high oven heat or broil will quickly caramelize the glaze; boiling water ready means you can cook noodles while the fish finishes.)

Cook the soba noodles according to package directions (usually 4–5 minutes) until al dente. Drain and immediately rinse under cold water until cool—this stops cooking, washes away excess starch and prevents the noodles from sticking. Toss the rinsed noodles with 1 tsp sesame oil and the white parts of the scallion to keep them glossy and aromatic. Keep warm or at room temperature. (Why: rinsing preserves the firm, nutty chew characteristic of soba and the sesame oil adds fragrance without making them greasy.)

Blanch the green beans: add the trimmed beans to the boiling pot and cook 2–3 minutes until bright green and just tender-crisp. Immediately transfer to an ice bath (bowl of ice water) to stop cooking and preserve color and crunch. Drain and pat dry. (Why: blanching cooks beans quickly and evenly while chilling locks in color and prevents overcooking when you finish them in the pan.)

Toast the sesame seeds in a dry skillet over medium heat for 1–2 minutes until they’re fragrant and just golden, shaking the pan constantly to avoid burning. Transfer to a small bowl. (Why: toasting releases the natural oils and deepens the nutty flavor—unt toasted seeds are flatter in taste.)

Sear the cod: heat a large ovenproof nonstick or stainless steel skillet over medium-high heat and add 1 tbsp neutral oil. When shimmering, place the cod fillets in the pan and sear 1–2 minutes to develop a light golden surface—don’t move them. Flip, glaze the top of each fillet with the remaining miso glaze and transfer the skillet to the preheated oven for 5–6 minutes until the glaze is slightly caramelized and the fish flakes easily. (Why: the initial sear creates a Maillard crust that adds flavor; finishing in the oven cooks the fish gently through while the glaze caramelizes under dry heat.)

While the cod is in the oven, finish the green beans: heat the same skillet on medium (wipe out excess fond if needed), add the remaining 1 tsp sesame oil and the minced garlic and remaining grated ginger; cook 20–30 seconds until fragrant (don’t brown). Add the blanched green beans and toss 1–2 minutes until warmed and lightly glazed. Season with a pinch of salt and a few drops of the broth from the noodle pot or a splash of water to loosen any fond. Stir in half the toasted sesame seeds. (Why: briefly sautéing the blanched beans with garlic/ginger warms them through and marries flavors; adding a touch of liquid dissolves any miso residue and creates a gloss.)

Check the cod for doneness: the flesh should flake with a fork and feel just opaque. Aim for an internal temperature of about 54–60°C (130–140°F) for moist fish—if you prefer USDA-recommended doneness, cook to 63°C (145°F). Remove the fish to rest 1–2 minutes. (Why: resting lets juices redistribute and the glaze set; an instant-read thermometer gives the most reliable doneness.)

Assemble: divide the soba between two shallow bowls. Arrange the sesame green beans alongside the noodles, then place a miso-glazed cod fillet on top. Spoon any remaining pan juices over the fish and noodles. Sprinkle with the remaining toasted sesame seeds, the green parts of the scallion, and chopped cilantro or parsley. Finish with a light drizzle of sesame oil and more cracked pepper to taste. (Why: layering noodles, vegetables and fish lets each bite include contrast in texture and flavor; the final herb and sesame brighten and round the dish.)

Serve immediately. (Why: the miso glaze is most vibrant right after cooking; noodles will firm as they cool.)