MELT 2/3 of dark chocolate in uncovered, microwave-safe bowl on HIGH (100%) power for 45 seconds; STIR. If pieces retain some of their original shape, microwave at additional 10- to 15-second intervals, stirring just until melted. Add remaining dark chocolate and stir until melted. Spread chocolate into 10 x 8-inch rectangle on prepared baking sheet.
MICROWAVE white morsels in small, heavy-duty plastic food storage bag on MEDIUM-HIGH (70%) power for 30 seconds. Knead bag until morsels are smooth. Add oil; knead to combine. Cut tiny corner from bag; squeeze to drizzle over dark chocolate. Immediately sprinkle chopped cookies over bark.
REFRIGERATE for 30 minutes or until firm. Break bark into 24 pieces. Store in airtight container at room temperature for up to 1 week. Cook's Tip: 1 1/4 cups NESTLÉ TOLL HOUSE Semi-Sweet Chocolate Morsels may be used in place of dark chocolate baking bars.