My first foodie recommendation for Lisbon is the Time Out food market in an old market hall - Mercado da Ribeira. It brings together a careful selection of the cities finest restaurants, bars, cafes and chefs in a sociable setting. It's a cool place with a nice vibe and each stall follows the black and white design with a hint of their own branding, so it is very picture worthy. The whole place is a little more pricey than the rest of Lisbon in general (we got our mains and a drink for just under 15 Euros each) but you are getting the best tasty options.
I went for pad thai and sangria while Rob got some incredible pork from a local chef.