Line the base and sides of a 20cm square cake tin with baking paper - leaving paper hanging over the edges to help you remove the slice from the tin.
Pour the rice bubbles into a large bowl and set aside until needed.
Place the rice malt syrup and peanut butter into a small saucepan. Gently stir the ingredients over a medium heat until they have combined.
Remove the saucepan from the heat and quickly pour it into the bowl with the rice bubbles. Use a large metal spoon to carefully combine the ingredients. Make sure that all of the rice bubbles are coated with the peanut butter and rice malt syrup.
Once combined, pour the coated rice bubbles into the lined cake tin. Use two metal spoons to cover the base of the tin with the mixture and smooth the surface. Place the tin into the fridge.
If you are icing your slice, break the milk chocolate into small pieces and place it along with the vegetable oil into a microwave safe bowl.
Cook the chocolate for 30 second spurts until it has almost melted before removing the chocolate from the microwave and stirring until it has completely melted.
Remove the slice from the fridge and pour over the melted chocolate – to completely cover the slice you may have to turn the tin to allow the chocolate to run.
Place the slice back into the fridge and allow to set – this shouldn’t take much longer than an hour.
Once set, remove the slice from the fridge and cut into small squares.