If he's only curious about Good Friday, a New Testament would suffice. Or maybe "Christ the Conqueror of Hell" by Met. Hilarion Alfeyev, though I've not read it myself.
If he's more interested in Christianity in general, "Surprised by Christ" by Fr James Bernstein, a Jewish convert to Orthodoxy, might be of interest.
Thanks age234. I will check out your first suggestion, never heard of it myself. As for the second, I actually own a copy but I am reluctant to give it to him. I don't want to make it look like I am trying to convert him or anything...