The Mustard Seed Cafe at Sonairte is a small, very laid-back cafe that serves all freshly made, organic food. There is a soup of the day, different salads, wraps, desserts and fair trade tea and coffee.
The staff is very helpful and friendly. The prices aren't that high either. For a soup with bread you would pay about 4€.
Most of the food is vegan or can be made vegan.
Sonairte is well worth a day trip. As ecology centre the offer courses on sustainable living and other things. There is a big garden, a nature trail, a little museum and an eco shop as well as the cafe.
Take the bus (Matthew's bus services) heading for Drogheda from Parnell Street in Dublin 1. It takes about half an hour. Just tell the driver where you want to go and he will tell you when to get off.