Line a 9×13″ baking dish with aluminum foil, shiny-side up. Melt chocolate in the microwave in 30 second intervals on half power, stirring between each, until chocolate is just melted through. Stir in peppermint extract, then pour into baking dish and smooth into an even layer.
Scatter crushed oreos and candy canes all over melted chocolate, gently pressing them into the chocolate. Let chocolate harden at room temperature, about 1 hour. Lift the bark out of the pan using the foil and break into pieces. Store in an airtight container at room temperature.