Prepare a grill for medium heat; lightly oil grate with vegetable oil. Pat one 2¾–3-lb. whole skin-on side salmon dry with paper towels, then place, skin side down, on a paper-towel-lined baking sheet. (You want to catch any excess oil when you brush the salmon, as it can cause flare-ups that will char the skin faster than the flesh can cook.) Carefully brush 1–2 Tbsp. extra-virgin olive oil, depending on the size of the fish (err on the side of less oil), over flesh side of fish; season generously with kosher salt.
Place salmon on grate, skin side down, and cover. Grill,
undisturbed, until skin is lightly charred and crisp and flesh is opaque, 20–23 minutes.
(To check for doneness, slide a butter knife into the thickest part of the fish, pull it
out, and hold a flat side to the back of your hand; it should be very warm). Using 2
spatulas, slide fish onto a platter. Increase grill heat to medium-high.
While the salmon is grilling, mix together 1 large jalapeño, ribs and seeds removed, finely chopped, 3 garlic cloves, finely grated, 1 cup coarsely chopped parsley, ¾ cup coarsely chopped unsalted roasted almonds, ¼ cup fresh lemon juice, ½ tsp. ground cumin, and ⅓ cup extra-virgin olive oil in a large bowl. Season almond mixture generously with salt and freshly ground pepper.
Place 4 poblano chiles, halved, ribs and seeds removed, in a medium bowl and drizzle with extra-virgin olive oil; turn to coat. Arrange, skin side down, on grate and cover. Grill until well charred, 8–10 minutes. Let peppers cool slightly.
Drizzle cut sides of 1 lemon, halved, with extra-virgin olive oil. Grill, cut side down, until lightly charred, about 2 minutes.
Rub off charred skin from chiles; discard. Coarsely chop
flesh; stir into almond mixture; spoon romesco over salmon. Serve with lemon for