Preparation: Line a baking sheet with parchment paper. Ensure there's enough space in your refrigerator for the baking sheet.
Place the semi-sweet chocolate chips in a microwave-safe bowl. Microwave at 50% power for 60 seconds, then stir. Repeat this process twice more, for a total of 3 intervals, stirring after each until the chocolate is smooth and creamy.
Spread the melted chocolate onto the prepared baking sheet, aiming for an even layer about 1/8" thick. Refrigerate until the 1st chocolate layer becomes firm.
Once the chocolate layer is firm, melt the white chocolate chips in another microwave-safe bowl using the same method as the semi-sweet chocolate chips.
After melting, gently fold in 1 cup of crushed peppermint candies and the peppermint oil, mixing thoroughly. Carefully spread this mixture over the firm chocolate layer. Sprinkle the remaining crushed peppermint candies on top.
Refrigerate the layered chocolate bark until completely hard. Once set, remove it from the refrigerator and use a sharp knife to cut the bark into triangular pieces.
Serve the peppermint bark immediately or cover and store at room temperature until ready to serve.