Heat the oven to 425F (220C) with a rack in the upper third. Line a sheet pan with foil or parchment. Pat the salmon dry, season with the salt and set it on the pan, skin side down if there is skin.
In a small bowl, stir together the gochujang, honey, soy sauce, rice vinegar, sesame oil, garlic and ginger until smooth. It should be thick enough to cling to a spoon. If your gochujang is very stiff, loosen with a teaspoon of water.
Spoon about two thirds of the glaze over the top and sides of the salmon and spread it with the back of the spoon. Keep the rest for later.
Roast for 8 minutes. Pull the pan out, brush on the remaining glaze, then switch the oven to broil (grill) on high and cook another 2 to 4 minutes, until the glaze bubbles and chars at the edges. Watch it closely, the honey goes from dark to burnt fast.
Check the thickest part. The salmon should flake with gentle pressure but still look slightly translucent in the very centre, about 125F (52C) on a thermometer. Rest 2 minutes on the pan.
Scatter with sesame seeds and scallions and serve with rice and kimchi or a plain cucumber salad.