Panino con soppressa vicentina is built on the large, soft Vicenza salame, and the word to hold onto is soft. The soppressa vicentina is a wide, fat-flecked pork salame from the Veneto, ground coarse, generously fatty, scented with garlic and a little pepper, and aged slowly so it never sets hard the way a small dry salame does. Cut thick, a good slice gives slightly under the knife and turns almost yielding at room temperature, sweet and lardy rather than tangy or sharp. This is the defining fact of the sandwich: it is not the firm spiced soppressata of the South spelled differently, but a separate Veneto thing entirely, broad and pillowy and mild, and the bread is chosen to stay out of its way.
The craft is in the thickness of the cut and in the temperature. A meat this soft is sliced thick on purpose, two or three millimetres rather than paper-thin, because shaving it to vapour loses the very tenderness that distinguishes it; you want a slice with body that compresses gently into the crumb. It is brought to full room temperature before it goes in, since cold flattens the garlic and tightens the fat, while warmth lets both bloom. The bread is a plain Veneto roll or a piece of soft country loaf, crust enough to hold the structure but never assertive, because an aggressive bread would argue with a salame whose entire character is its mildness. Dressing is close to nothing: no oil, no condiment, perhaps a wedge to eat alongside, the discipline being to let one soft fatty meat be the whole sandwich rather than half of one.
The variations are about pairing and what the Veneto puts beside it. The classic table version is soppressa with a hunk of bread and a glass of local red, no sandwich engineering at all; another build sets it against fresh soft cheese or grilled polenta rather than a roll. The other pressed and coarse-ground salami of Italy, the firm spiced Calabrian, Lucanian, and Molisan soppressata and the gelatinous Tuscan soprassata, are different animals on different breads. Each deserves its own article rather than being crowded in here.