Pat the salmon dry. Season lightly with salt and pepper. If your soy sauce isn’t low sodium, go easy on the salt.
Make the glaze base. In a small bowl, whisk soy sauce, brown sugar or honey, mirin, rice vinegar, ginger, garlic, and sesame oil.
Reduce the sauce. Pour the mixture into a small saucepan. Bring to a gentle simmer over medium heat and cook 4–6 minutes, stirring occasionally, until glossy and slightly thickened.
If using cornstarch, stir in the slurry and simmer 30–60 seconds more. Set aside.
Sear the salmon. Heat the neutral oil in a large skillet over medium-high. Place salmon in the pan, skin-side up if using skin-on.
Sear 2–3 minutes until you see a golden edge.
Flip and glaze. Turn the salmon. Reduce heat to medium-low. Spoon some glaze over each fillet and cook 2–4 more minutes, basting as it cooks.
The salmon should flake easily and be just opaque in the center. Aim for 125–130°F internal temperature for medium.
Optional broil finish. For extra caramelization, transfer salmon to a foil-lined sheet, brush with more glaze, and broil 1–2 minutes. Watch closely to avoid burning.
Rest and garnish. Let the salmon sit 2 minutes.
Top with sesame seeds and green onions. Serve with rice, steamed broccoli, or a crunchy slaw. Pass extra glaze and citrus wedges at the table.