Drop the pretence that this is anything other than what it is and the sandwich immediately gets better. Surimi is a processed paste of white fish, usually pollock, washed, minced, bound with starch and egg white, flavored, and formed into the pink-striped sticks sold to imitate crab. It is not crab and it does not taste like crab, but it is mild, faintly sweet, springy, and inexpensive, and treated as its own ingredient rather than a substitute it makes a clean, light sandwich. The build is a baguette or a soft roll, surimi sticks shredded or sliced, and a binding of mayonnaise brightened with lemon.
The logic follows from the texture and the price. Surimi is uniform, holds together, and carries dressing well, so the sandwich is fast to assemble and consistent in a way that real shellfish, with its perishability and its variable quality, is not. That reliability is the whole appeal: this is the budget reading of the seafood sandwich, and it earns its place by being dependable rather than by aspiring to something it is not. The flavor is gentle, so the build leans on its supports: mayonnaise for richness and to bind the shredded sticks into a cohesive layer, lemon for the acid that keeps it from going bland, black pepper and sometimes a little chopped herb or chive for definition. Without the acid and salt the filling reads flat, since the surimi itself contributes mildness more than flavor.
The bread does little except hold the dressed filling without crushing it. A soft roll or a tender baguette works; the surimi is bound loose rather than packed dense, so the spring survives to the bite. There is no warm component and no real waiting, though the dressed filling is best made close to service so the bread does not go slack under the mayonnaise.
Variations move along the binding and the additions. A crème fraîche dressing reads lighter and tangier than mayonnaise; a spoonful of diced cucumber or a leaf of crisp lettuce adds crunch against the soft sticks; a touch of lemon zest sharpens it. It belongs with the fish sandwiches the catalog groups under Baguette Poisson, and its specific contribution is the candid budget option: a mild, springy, formed-fish filling that makes a decent sandwich precisely when it is taken on its own terms.