A place worth eating in Lisbon is Time Out, a food court located in Lisbon's historic market hall – the Mercado da Ribeira – . You can find 35 permanent stalls from some of Lisbon’s most popular food shops and restaurants. A good stop to get some wifi and rest, as summer in Lisbon can be completely sofocating.
I wouldn't say it's cheap but I would recommed it to anyone.
credits: pictures taken and edited by me.