I don't really like lemon and chocolate pairings. One, because I'm just not huge on chocolate, but two because they're best left to shine on their own. That's why you get the expression about people being either lemon or chocolate when it comes to ordering dessert.
But if you must, you can do a lemon tart with a layer of chocolate. Suzanne Goin does one, though it's with sweeter Meyer lemons.
And truth be told, I didn't care for it because it just took away from the lemon tart. Yeah, I'm just not big on chocolate and lemon together.
You could also try chocolate and lemon caramels, but you'll use mostly zest, not whole lemons.
There's Pierre Herme's Riviera, but you might find it a little daunting to make all the components:
Plus it will cost you a decent sum since chocolate is a pricey ingredient.
Here's a tart with chocolate crust from Kate Zuckerman:
Well, there is chocolate-dipped candied peel. I like that okay (though I prefer orange peel), but it does involve candying and tempering chocolate, which are a bit intimidating for a lot of people.
I prefer white chocolate pairings with lemon. The lemon tempers the sweetness of the white chocolate pretty nicely. Don't know if you're interested in that.