Prep the salmon. Pat it dry and season both sides with salt and pepper. If using skin-on salmon, score the skin lightly to prevent curling.

Boil the noodles. Cook according to package directions until just shy of tender. Reserve 1 cup of the starchy cooking water, then drain and set aside.

Sear the salmon. Heat 1–2 tbsp oil in a large skillet over medium-high. Place salmon in the pan (skin-side down if applicable) and sear 3–4 minutes. Flip and cook 2–4 minutes more, depending on thickness, until just opaque in the center. Transfer to a plate to rest.

Make the miso butter base. Lower heat to medium. Add 2 tbsp butter to the same pan. Stir in garlic and ginger and cook 30–45 seconds until fragrant, not browned.

Build the sauce. Whisk in miso paste with the remaining 2 tbsp butter, soy sauce, and rice vinegar. Add a splash of noodle water to loosen into a silky sauce. Taste and adjust with more soy (salt), vinegar (brightness), or a touch of honey (balance).

Add vegetables (optional). Toss in a few handfuls of spinach or snap peas. Cook 1–2 minutes until just wilted or crisp-tender.

Flake the salmon. Gently break the salmon into large flakes, discarding skin if you prefer. Add to the pan and fold into the sauce.

Toss with noodles. Add the drained noodles and a splash more noodle water. Toss until coated and glossy. The sauce should cling, not pool. Adjust seasoning and consistency as needed.

Finish and serve. Top with scallions, sesame seeds, and a squeeze of lime. Add chili crisp or red pepper flakes for heat. Serve immediately.