Braga is in the Minho, a region that takes its food seriously. Caldo verde (kale soup with a slice of chouriço), bacalhau (salt cod) in dozens of preparations, and roast veal are the staples. The old centre has a good cluster of restaurants around Largo do Paço and Rua do Souto; the university area north of the centre is cheaper and livelier.
Try Taberna Belga for traditional Minho cooking in a casual setting, or Cozinha da Sé for something smarter near the cathedral.