Salt the salmon at least an hour ahead, two to three hours is the sweet spot, and leave it uncovered on a rack in the fridge. About half a teaspoon of Diamond Crystal for a 6 oz fillet, skin and all, and that is the whole of the salt for the fish. If you are cooking right now, salt the fillets as they go into the pan instead.
Heat the oven to 450°F with a sheet pan inside it.
Cut the broccoli through the stem so every piece has one flat face. Toss it in a bowl with the olive oil and salt until every face is glossy. Tip it onto the hot pan and turn every piece cut face down, in a single layer with space around each one. Roast 15 to 18 minutes without moving it.
When the broccoli has about twelve minutes left, set a skillet over medium-high. Little to no oil: this fish is fatty enough to grease its own pan inside the first minute.
Pat the salmon skin completely dry.
Lay the fillets in skin down, away from you, and press them flat for 30 to 60 seconds. They should sizzle the moment they land. No sound at all in the first ten seconds means the pan was not hot enough, so lift the fillets out, let it come up, and lay them back in. Then drop the heat to medium.
Cook 3 to 4 minutes skin down. You want a steady fine crackle. A loud, hard sizzle means the heat is too high, so lower it a little.
Take the pan off the burner. Lift the fillets onto a rack, skin side up, and leave them 4 minutes.
Pan back on medium. Return the fillets skin down for 3 more minutes, then flip for 1. Pull at 130°F.
Spoon 1 tablespoon of snap pea pesto into the center of each plate. Set the fish on it, skin up. Broccoli alongside.
Serve with lemon at the table.