Line a lamington tray 18 x 18cm with baking paper. Place the chocolate in a large heatproof bowl. Melt the chocolate using a microwave, approximately 1 minute on high. (This will vary depending on the strength of your microwave).
Add the remaining ingredients to the melted chocolate and combine until the ingredients are coated in chocolate. Then immediately pour the mixture into the lamington tray. Use a wooden spoon or spatula to spread the mixture out evenly and top with a few remaining peanuts, cube lollies and marshmallows as desired for decoration.
Transfer to the rocky road slice to the refrigerator to set before cutting into bite size squares using a warm knife.