Dramatic and foolproof, this dish is made for entertaining dinner guests. Cover the grill while cooking and you won't need to stress over flipping the fish—and the results will be perfectly cooked every time.
Heat grill to medium; brush grates with vegetable oil. Drizzle both sides of salmon with olive oil; season with salt and pepper. Place salmon on grill, skin-side down, and cover. Grill, without moving fish, until just opaque in center and skin is crisp, 7 to 9 minutes. Using 2 spatulas, transfer fish to a platter. Drizzle lemon rounds with olive oil; grill until lightly charred, about 2 minutes a side. Transfer to platter; sprinkle with fennel fronds. Serve, with relish.