The eggplant grinder is the meatless parm that has to work harder than the meat version, because eggplant gives up water under heat and the sandwich is a fight against that water reaching the roll. Breaded and fried eggplant, marinara, and melted cheese on a New England grinder roll is the build, and the engineering question is keeping a vegetable that sweats inside a hot, saucy sandwich from turning the bread to mush. The grinder roll, split and toasted, is the answer to a problem the chicken parm never has to solve as severely.
The craft is in the frying and the assembly order. The eggplant is sliced and salted to pull moisture before it ever hits the breading, then breaded and fried hot so the coating sets into a shell that resists the sauce around it. The grinder roll is a sturdy Northeastern sub length with a crust that holds structure under a wet load, and it is toasted before assembly so the cut faces firm into a partial barrier against the marinara. The sauce is kept tight rather than loose, the cheese laid so it melts into a seal over the eggplant, and the whole thing is run under heat just long enough to bind it without flooding the bread. The reward when it is timed right is the contrast that defines it: the fried coating still has snap against the soft interior of the eggplant and the give of the roll, instead of the entire sandwich collapsing into one wet texture.
The variations keep the meatless logic. A version layers fresh mozzarella for stretch over the sharper grated cheese; another adds roasted peppers or broccoli rabe for a bitter edge against the sweet sauce; a baked-not-fried version trades the crisp shell for something softer. The chicken and meatball builds on the same roll are close relatives that change the center. Each of those is its own build and deserves its own article rather than being crowded in here.