01 - Strain the watermelon juice through a fine mesh sieve to remove all pulp and seeds, ensuring a completely smooth liquid base.
02 - In a medium saucepan, whisk together the granulated sugar and cornstarch until thoroughly blended and no lumps remain.
03 - Gradually pour the strained watermelon juice into the saucepan while whisking continuously to prevent clumping and achieve a smooth mixture.
04 - Stir in the lemon zest and vanilla extract (or vanilla powder) until evenly distributed throughout the mixture.
05 - Place the saucepan over medium heat and stir constantly. Cook for 8 to 10 minutes until the mixture thickens to a soft pudding consistency, coating the back of a spoon.
06 - Remove from heat and gently fold in the dark chocolate chips or chopped chocolate, allowing them to soften and create traditional 'seed' appearance.
07 - Pour the pudding into individual serving glasses or molds. Allow to cool completely to room temperature, then refrigerate for at least 3 hours until fully set.
08 - Just before serving, sprinkle each portion with finely chopped pistachios. Add dried rose petals and additional chocolate chips as desired for presentation.