Begin by lining a baking sheet with parchment paper, ensuring that it is smooth and flat to prevent sticking.
In a double boiler or microwave-safe bowl, melt the finely chopped dark chocolate, heating in 20-second intervals if microwaving, stirring until smooth.
Remove the dark chocolate from heat and stir in the puffed quinoa or tiny puffed rice until evenly coated. Spread the mixture onto the prepared baking sheet in an even layer. Set aside.
Melt the finely chopped white chocolate using the same method. If using cocoa butter, add it now for a smoother consistency.
Sift in the matcha powder and whisk until fully incorporated and the mixture is a vibrant green.
Pour the matcha white chocolate mixture over the dark chocolate layer, spreading evenly with a spatula. Swirl the two chocolates together slightly for a marbled effect if desired.
Sprinkle sprinkles or other decorations over the top if using, adding color and visual appeal.
Place the baking sheet in the refrigerator for 1 to 2 hours until the bark is fully set.
Once set, lift the bark off the parchment paper and break it into pieces of your desired size.