Line a 28 x 18cm slice tin with baking paper, making sure you leave paper hanging over the sides.
Add the biscuits to your Thermomix bowl and mix for 10 seconds, speed 8 to crush. Transfer to a separate bowl until needed.
Without washing the bowl, add the condensed milk and butter to your Thermomix bowl and cook for 3 minutes, 60 degrees, speed 2 or until melted and combined.
Add the crushed biscuits, lemon zest and coconut to your Thermomix bowl and mix for 10 seconds, speed 4 to combine. Scrape down the sides of your bowl and mix for a further 5 seconds, speed 4 to combine.
Pour the mixture into your prepared slice tin and use the back of a spoon to press the mixture into the tin before placing it into the fridge for 30 minutes to chill.
To make the passionfruit icing, place the icing sugar, passionfruit pulp and butter into a clean Thermomix bowl and mix for 10 seconds on speed 3 to combine. If your icing is a little thick, add a teaspoon of water.
Pour the icing over the chilled slice base and use a butter knife to help spread it across the slice.
Place the slice back into the fridge for three hours (or until the icing has set) before cutting into squares to enjoy.