We traveled in August of last year. There were 2 vegetarians and two omnivores. We were traveling for a little over 3 weeks. We found it to be hit or miss as far of menu options go. Some places listed the vegetarian special - that was pretty much you get what you get and don't get upset plate of food. But for the most part we throughly enjoyed our meals when in Ireland and if there was not a huge selection of veg dishes offered the restaurant's ambiance and service more that made up for the limited food selection. Here is our list of places we ate:
Dublin: We had great vegetarian food in Dublin. This will be the easy one!
Kinsale: We ate at Fishy Fishy - looking at the current menu I have no idea what we ordered when we dined there. But whatever we ate is was delicious. I mostly wanted to eat there because Phil of "I'll Have What Phil's having" filmed there. You can probably find a more veg friendly place.
Dingle: Ashe's Pub and Doyle's Seafood - Both offered one or two veg dishes but they were both delicious. I would recommend either one. The service was excellent. Reservations recommended at both.
Portrush: Recommend this one! Ocho Tapas Bistro - fantastic tapas place with a nice selection of vegetarian dishes. Reservation recommended.
We also ate the the Ramore Wine Bar - They don't have a huge selection of veg dishes but I do recall we were able to put together a very nice meal. Reservations Recommended