In a microwave-safe bowl, combine 2-1/2 cups vanilla chips and the chocolate chips. Microwave on high for 2 minutes. Microwave for 1-2 minutes; stir until smooth. Immediately add marshmallows, cereal and walnuts.
Spread evenly on a 13-in. pizza pan that has been coated with cooking spray. Arrange cherries on top; sprinkle with coconut.
Microwave the remaining vanilla chips on high for 1 minute. Add oil and stir until smooth. Drizzle over pizza. Chill until firm. Serve at room temperature.
Editor's Note: Recipe was tested in a 700-watt microwave.