In a large mixing bowl, combine the graham cracker crumbs and shredded coconut. Mix well until evenly combined.
In a separate bowl, melt the chocolate chips and butter together in the microwave in 30-second intervals, stirring in between until smooth.
Add the sweetened condensed milk and vanilla extract to the melted chocolate mixture, stirring until fully combined.
Pour the chocolate mixture over the graham cracker and coconut mixture. Add the mini marshmallows and gently fold everything together until well mixed.
Line an 8x8-inch baking dish with parchment paper. Press the mixture evenly into the prepared dish.
Refrigerate for at least 2 hours or until firm. Once set, lift the slice out of the dish using the parchment paper and cut into squares.