Pre-heat oven to 350 degrees. Grease a 6.5" cast iron skillet with coconut oil and set aside.
Combine black beans, maple syrup, peanut butter, coconut oil, almond milk, and vanilla in a food processor or powerful blender. Blend until smooth, then add all remaining ingredients except chocolate chips.
Remove batter from food processor and fold in chocolate chips. Scoop batter into greased skillet and spread evenly. Top with a few extra chocolate chips if desired and push down slightly into the top of the batter.
Bake at 350 degrees for about 20 minutes or to desired done-ness. (A couple minutes less will yield a more lava cake-like center and a few more minutes will yield a less gooey center.)
Allow cake to cool for several minutes, then top with marshmallow fluff and miniature marshmallows. Toast using a kitchen torch, then top with graham cracker crumbs and melted chocolate, if desired, before serving.
To make this more brownie-like, skip the baking powder!
I used this cast iron skillet.