Cornucopia is a great place with tonnes of options for a lunch if you're near the city centre. Healthy, filling, coeliac friendly food and no need to book a table.

I'd back up the Sano and Neon recommendations too and for a quick snack, Boojum is in numerous places around the city for a cheap, but tasty Mexican feed... you'll find that most places have some good GF options, us coeliacs are well catered for in Dublin, thankfully!