Remove tough, outer layers of lemongrass. Chop remainder really fine, with a knife or in a small food processor. Mix lemongrass with olive oil.
Season salmon liberally with salt on both sides. Place in a shallow dish. Pour lemongrass and olive oil mixture over flesh side of fish. Refrigerate uncovered 20 minutes or up to overnight.
Heat grill on high; then reduce heat to medium-high. Place salmon flesh side down. Cover and cook 3 minutes. Flip and cook, covered, an additional 3 to 5 minutes, or until flesh is flaky and opaque.
