I've looked online at recipes, but can't tell what makes for a good one for this pie. The one I had awhile back was dense, very chocolatey, but not at all wet (like with underdone brownies).
I always think of chess pie as having that gooey texture
you are trying to avoid. To me, whether plain or chocolate, the texture is similar to pecan pie with a natural slightly crunchy crust on top. If you're looking for something less gooey, maybe look at brownie pie recipes. I've linked one that from the picture looks more solid than a chess pie. It's similar to one I've made, but I use regular chocolate and not mint flavored. Hope that helps!