Sprinkle gelatin over cold water and let sit for 2–3 minutes until thickened.
Pour hot green tea over gelatin and stir until completely dissolved.
Add lemon juice, sweetener, and matcha powder if using, then mix well.
Transfer mixture into silicone molds or a small dish.
Refrigerate for at least 2 hours until fully set.
Remove from molds or cut into cubes and serve chilled.
