Somewhere different, interesting, and really pleasant to visit in Tortosa is L'Assoc taverna/restaurant.
It is in C/Major de Sant Jaume 6, which is in the old quarters, and was formerly Arab baths, and then an olive oil mill.
They serve tapas, also menu del dia which cost 10 euros.
Evening menus, and special menu on Friday and Saturday evenings serving entrecot (steak) for 20 euros including wine. Closed Mondays.