Preheat oven to 180°C. Line a slice tray with baking paper.
Place weet bix, coconut, flour, baking powder, sugar, salt and zest into the Thermomix bowl. Combine 5 sec/speed 5.
Add butter and vanilla. Combine 5 sec/speed 5.
Spread into the prepared tray and smooth surface with a spatula. Bake 15 minutes. Cool.
To make the frosting, place all ingredients into the Thermomix bowl and combine 10 sec/speed 5.
Place in fridge to set. Slice into squares and garnish each piece with an edible flower if desired.