How do I cook any recipe with frozen eggplant?
If the slices are thin, you could bake/roast straight from frozen. I do believe the texture will be quite soft so use a parchment lined sheet if you wish to roast it. I like to brush a bit of miso mixed with honey on roasted eggplants. 

Another option would be to lay it into a lasagna. I think this option is the most appealing. I wouldn't bother to thaw it if your slices are under half an inch thick. 

If you sliced it only in half, such that you have two "boat" shaped halves, I would thaw it fully first. It'll take a while to thaw in such large pieces. Baba ganoush would be a good option in this case.