Cool the garlic until it can be handled. Peel it and place in a blender, along with the guajillo chiles (including their soaking liquid), the chipotles and peanuts. Blend until nearly smooth, then scrape into a small bowl. Stir in a little more water if necessary to give the salsa an easily spoonable consistency. Taste and season with salt, usually about 1/2 teaspoon.
Heat a gas grill to medium-high or light a charcoal fire and let the coals burn until covered with white ash and very hot. Smear salmon fillets and green onions with a little oil and sprinkle with salt. On coolest part of grill (usually toward an edge), grill onions, turning regularly, doing best to keep the green parts farthest from the heat, until soft, about 10 to 15 minutes.
Lay salmon fillets on hottest part of grill, placing what had been their skin side down. When grill grate has deeply seared marks into salmon and salmon has begun to release itself from the grate, after about 3 minutes, depending on heat of the fire, flip the fillets and cook to desired degree of doneness, usually a couple of minutes longer for 1-inch-thick fillets to reach medium. Transfer to warm dinner plates.
Chop green onions into small pieces. Spoon some salsa over each fillet, sprinkle with chopped onion and serve right away.