A day or two before, make the marinade: Mix ingredients in a bowl and chill.
About 1 1/2 hours before dinner, deputize a guest to prep rice, lettuce, and cilantro while you pour half the marinade into a pan large enough for salmon. Pat fish dry and set, flesh side down, in marinade. Chill 45 minutes.
Heat a grill to medium-high (450°) with an area cleared (for charcoal) or a burner turned off (for gas) to make an indirect-heat area. Fold a large sheet of heavy-duty foil in half. With a knife, poke dime-size holes in foil 2 in. apart. Oil one side of foil. Brush salmon skin with oil.
Set foil on grill over direct heat, oiled side up; heat 2 minutes. Place salmon, skin-side down, on foil. Cook, covered, until skin is light brown and sizzling, 5 to 6 minutes. With tongs, slide salmon on foil to indirect-heat area and cook, covered, until all but top 1/4 in. is cooked, 3 to 8 minutes. Slide back to direct heat and cook until skin is well-browned and crisp, 2 to 3 minutes. Transfer salmon on foil to a rimless baking sheet.
With the help of your deputy cook, slide a large metal spatula between foil and salmon skin to free skin. Carefully slide salmon from foil to a platter. Season with salt, drizzle with some remaining gochujang marinade, and scatter sesame seeds on top.
Together, serve it forth: Set the salmon on the table with rice, lettuce, cilantro, remaining gochujang sauce, and Fresh Bean Sprout Banchan.
*Find gochujang at well-stocked grocery stores and Asian markets. Use tweezers to pull out each salmon pin bone in same direction the bone is slanting.