The lomi lomi salmon sandwich is built on a filling that is already a finished dish, and the defining decision is leaving it that way. Lomi lomi salmon is salt-cured salmon hand-massaged with tomato, sweet onion, and green onion into a cold, loose, relish-like mixture, eaten on its own across Hawaii as a side. The sandwich does not cook it, dress it, or rework it; it carries it. That restraint is the whole idea: the cure and the massage did all the seasoning work before the bread ever entered, and the sandwich is a vehicle for a salad that stands complete on its own.
The craft is entirely in managing moisture, because lomi lomi is wet by nature. The salt cure firms the salmon and the hand-massaging, the lomi lomi itself, breaks the fish and the tomato down until they weep, so the mixture carries liquid that will run straight through soft bread. The build answers this two ways: the salmon is drained before it goes on, and the bread is a sturdy slice or a roll chosen to absorb the edge that escapes without collapsing, often with a leaf of lettuce as a barrier between the wet relish and the crumb. The flavor is already balanced inside the filling, the salt of the cure against the acid of the tomato and the bite of raw onion, so the sandwich adds almost nothing and is judged on whether it holds together long enough to eat. It is the plate-lunch and home-table reading of a dish that did not start as a sandwich, made sandwich-shaped without losing what it was.
The variations are mostly the carrier and how far the relish is drained. A tighter, well-drained build holds in hand like a cold sandwich; a looser one served open is closer to lomi lomi spooned onto toast. It belongs to the Hawaiian plate-lunch shelf and the broader American fish sandwich family, separate answers to putting cured or cooked seafood on bread, and those relatives deserve their own articles rather than being crowded in here.