Preheat and Prepare: Preheat your oven to 350 degrees F (175 degrees C). Line an 8 by 8-inch pan with parchment paper, leaving some overhang for easy removal.
Make the Crust: In a medium bowl, combine melted vegan butter, sugar, and salt. Add flour and mix until a thick dough forms. Press the dough evenly and firmly into the prepared pan. Bake for 16-18 minutes, until the edges are lightly browned. Set aside to cool.
Prepare the Filling: In a medium saucepan, combine lemon juice, lemon zest (if using), sugar, coconut milk, cornstarch, and a tiny pinch of turmeric for color (if desired). Whisk until the cornstarch is dissolved. Heat over medium, stirring constantly, until the sugar dissolves and the mixture thickens.
Layer and Bake: Spread the lemon filling evenly over the cooled crust, using a spatula to smooth it if needed. Bake for 15 minutes, then remove from the oven and cool at room temperature for 30 minutes. Transfer to the refrigerator and chill for 1-2 hours, or overnight, until set.
Cut and Serve: Once set, lift the bars out of the pan using the parchment paper. Dust generously with powdered sugar and cut into 16 squares.
Storage: Leftover bars can be stored in a covered container in the refrigerator for up to 1 week. They also freeze well. Enjoy your delicious vegan lemon bars!