The Sandwich Catalan is read in a Catalan register rather than a French one, which on the Roussillon side of the range means the bread is treated first. The defining move is the pa amb tomàquet logic: the cut face of the loaf rubbed with ripe tomato and a clove of garlic, then slicked with olive oil and salt, so the bread itself carries flavor before anything is laid on it. Onto that go the Catalan-leaning fillings of the Roussillon, usually a cured meat in the regional style, sometimes a sheep's-milk cheese, the components kept few and assertive.
The logic is that the bread is an ingredient, not a wrapper. The tomato rub soaks the crumb just enough to season it without making it wet, the garlic is a low note under everything, the oil binds it together, and the filling is asked only to sit on a base that is already doing half the work. The constraint is balance: the tomato-and-oil bread is soft and savory, so the filling has to bring salt and chew against it, which is why a firm cured meat or an aged cheese fits and a mild soft one disappears. The bread needs a real crust so it holds its shape once the cut side has taken on tomato and oil. There is no heat and no reason to wait beyond the moment the rub needs to settle into the crumb. This is a sandwich made close to service, the bread dressed first, the filling laid last.
Variations stay within the Roussillon vocabulary. A version built on cured pork in the Catalan style leans hardest on the salt-against-tomato contrast; one with a sheep's-milk cheese trades some of that salt for a denser, tangier register; the plainest is the tomato-and-garlic-rubbed bread with oil and almost nothing on it, the dressed loaf standing as nearly the whole sandwich. Each keeps the rubbed bread as the fixed point and changes only what it carries. The Sandwich Catalan sits with the place-named builds the catalog groups under Regional Specialty Sandwiches. Its specific contribution is the bread as a flavored base: a sandwich where the tomato and garlic go into the crumb before any filling is considered.