Z brick and real brick will take paint beautifully. I am painting more and more fireplaces all the time to a brilliant white.
This is a easy job, but takes many coats of paint. Here is what i do and use.
Clean off any debris or grease of stuff from the bricks. Being in the kitchen, I would be concerned about grease. Vinegar is great for this.
now, get a gallon of Zinzer B-I-N, a primer and start applying the stuff. Wait about an hour or so between coats. use a fan to speed up drying. you want to apply about 7 to 8 coats of primer to this surface. Paying particular attention to the mortar. A good job is when all the stuff is nice and smooth. Do not feel that this is a day or two project. The individual coats of paint must dry properly.
When this is done, now apply your Sherwin, or Ben Moore, or Kelly Moore paint. Use a good latex and use emanel or semi gloss. You want to apply about the minimum of 2 coats. you might see that additional coats make the work even better. This will not hurt a thing to load up coats, but just let each coat dry.
If you use a flat finish coat, you will not be pleased and it does not clean up well or at all. Use enamel or semi gloss only.
you will love your results and the room will be bright and clean looking.