Preheat your oven to 350F and line a baking dish with parchment paper.
In a mixing bowl, combine melted butter, sugar, flour and salt with a spatula until a dough forms.
Transfer the dough into the lined baking dish and press down using your hands or a spatula to create an even crust. Bake for 18 minutes, or until edges are golden brown. Remove from the oven and let cool.
In a saucepan over a medium heat, combine lemon juice, zest, sugar, coconut milk, cornstarch and vanilla. Whisk continuously while the mixture cooks, about 3-4 minutes. It will start to thicken up considerably (and create a hair gel-like texture), and you should be able to create stiff peaks when you remove the whisk from the mixture. Remove the mixture from the heat.
Sift the matcha powder into a small bowl and add 1/4 cup hot, but not boiling water. Use a bamboo matcha whisk or electric frother to incorporate the matcha into the water. The mixture should be relatively thick, as you don't want to add too much water to the lemon curd mixture. Once smooth, add to the pot and whisk in until smooth.
Pour the matcha lemon curd mixture over the shortbread crust and use a spatula to evenly spread the mixture out. It will set as you leave it so do make sure the top is smooth. Let the lemon bars cool to room temperature, then transfer to set in the fridge for 2 hours.
When ready to serve, dust with powdered sugar and cut into 14 pieces, or squares the size of your choice. Store leftovers in an airtight container in the refrigerator for one week, or freeze and let thaw to enjoy for up to 3 weeks.