Grease and line a 16X22cm rectangular slice tray with baking paper and set aside.
Place the biscuits into the TM bowl and roughly chop by pressing Turbo 5-10 times (you still want a few larger chunks). Remove and set aide.
In a clean TM bowl, place the condensed milk, butter and peppermint chocolate. Melt on 80 degrees, 3 minutes, Speed 2.
Add the cocoa powder and peppermint essence and mix on Speed 5, 10 seconds. Scrape down the sides of the bowl.
Add the crushed biscuits and mix on Reverse Speed 3 (using the spatula to assist) until combined (you may need to scrape down the sides of the bowl and repeat).
Spread mixture into a baking paper lined slice pan.
Melt the chocolate and coconut oil in a clean Thermomix bowl on 80 degrees, 3 minutes, Speed 2.
Pour the chocolate over the slice.
Working quickly, add a couple of drops of green food colouring to the white chocolate and swirl with a skewer.
Place the slice into the fridge until it feels 'tacky' but the chocolate hasn't set completely hard.
Take out of the fridge and slice into squares. Store in an airtight container for up to 5 days.