Coat a 13 x 9 x 2-inch pan with nonstick vegetable-oil cooking spray.
Melt the margarine in a large saucepan over low heat. Add the marshmallows; stir until the marshmallows are completely melted. Remove the saucepan from the heat.
Add rice cereal and candy to saucepan; stir until well coated.
Using a buttered spatula or waxed paper, press the mixture evenly into the prepared pan. When cool, cut into 24 bars.