Add matcha green tea powder, vanilla extract, salt, and sweetened condensed coconut milk. Mix well. Turn off the heat.
Add brown rice crisps cereal in batches. Mix well.
Spread the mixture into a parchment paper lined 9" x 13" baking dish.
Push down the mixture with damp hands. Cover and place in the fridge.
In a small bowl add powdered sugar and soy milk. Whisk until all the lumps are out. Place in the fridge for about 30 minutes to thicken.
After the icing thickens, pull the rice crispy treats out by the parchment paper. Slice lengthwise, then slice into triangle shapes.
Sprinkle rainbow sprinkles on each rice crispy treat. Drizzle icing in a criss-cross pattern. The icing will harden after sitting out at room temperature or after being placed in the fridge.
Notes
Store in an airtight container. They will last 3-4 days at room temperature and a week in the fridge. They will stay soft because of the sweetened condensed coconut milk.