Preheat the oven 10 160 degrees Celcius for fan forced (or 180 degrees without a fan)
Process your Weetbix in a food processor or Thermomix until finally crumbed (this talks me three quick pulses in my Thermomix on turbo)
Pour crumbs into a bowl.
Add cocoa, coconut and sugar and combine.
Add melted butter and egg and combine.
Line a square tin (20cm x 20cm) or a slice tin (15cm x 30cm) with baking paper
Press the mixture firmly into the tin, making sure to push firmly around the edges and corners.
Place in the oven and cook for 20 minutes.
Remove from the oven when firm and let it cool.
Melt the chocolate and stir in the coconut oil. The oil stops the chocolate from setting hard. If you prefer a hard chocolate top then leave out the coconut oil.
Pour the melted chocolate mixture over the top of the slice, making sure to cover the whole slice. I find the best way to do it is to tip the tin to let the chocolate run each way.
Check on the slice about 45 minutes after putting it in the fridge. Sprinkle your coconut on top if the chocolate looks to be setting (if you sprinkle it when it's really wet it just sinks in).
Refrigerate the slice for around 1.5 hours. Once the chocolate top is set you can take it out and slice it up. Feel free to add a bit more coconut if you like too! Store it in an airtight container in the fridge.