Preheat the oven to 350 degrees F. Place paper cupcake holders in a muffin tin, Line each paper cupcake holder with 1 cracker. Top with a layer of chocolate pieces - the chocolate should lie flat. Sprinkle the chocolate with chopped walnuts and coconut flakes. Place another cracker on top. Bake for 10 to 15 minutes, until the chocolate is melted. Remove from theoven and gently push the top cracker into the chocolate to make it stick securely. Cover the top crackers with mini marshmallows and bake for another 7 to 8 minutes, or until the marshmallows have browned. Remove from the oven and set aside for 15 minutes before removing from the wrappers.