If you like greek food, a good place to eat in Costa Mesa is Daphne's Greek Cafe. Daphne's is a chain and I know there are many locations in Orange County. My compliments have to go out to the Costa Mesa Restaurant on Harbor.
My co worker and I love to have lunch here. You walk in and the lines are long sometimes, but it goes by fast. Once you order you get your drink and sit at a table. They have plenty of outdoor tables too if you like to tan and eat :o). The food is brought out to you like a full service restaurant. There are no waiters but the staff is so attentive and came out twice to make sure we did not need anything.
The Restaurant is clean and the price for their lunch specials is a good value.
If you are in a rush. Go to their website and order your food on line. You not only get a free drink if you order on line. But your order will be ready when you get there.