Crush oreo cookies into small chunks (we put them in a plastic bag and rolled them with a rolling pin until they were in relatively small pieces).
In a medium bowl, melt milk chocolate chips in 30 second intervals, stirring between each one, until the chocolate is smooth. Add the crushed oreos, and stir to combine.
With a large spoon or spatula, spread the chocolate oreo mixture into a rectangle on the prepared baking sheet until the chocolate is about 1/4-1/8" thick. Set aside.
Melt the white chocolate chips in 30 second intervals, stirring between each one, until the chocolate is smooth. Reserve about 1/4 cup of the melted white chocolate in a small plastic bag to drizzle on the top. With a spoon or a spatula, spread the remaining white chocolate over the top of the milk chocolate until covered.
Place the candy eyes on top however you like.
Cut a small corner off the plastic bag and drizzle the reserved white chocolate on top.
Freeze for 10 minutes, then remove and cut (or break) into pieces.
Notes
You can modify this recipe by using other Halloween-theme candy to decorate the bark, or use Halloween-colored food dye for the icing.