Place quinoa and 1⅓ cups (325 mL) of the rice beverage in a small pot and bring to a boil. Cover, reduce heat to medium-low, cook undisturbed 15 min., or until the quinoa is tender and liquid has evaporated. Spoon quinoa into a bowl to cool.
Preheat oven to 350F (180 C). Lightly grease 9-in. (23 cm) springform cake pan. Line bottom of pan with parchment paper.
Sift cocoa powder into a large bowl. Whisk in sugar, baking powder and salt.
Place remaining ⅓ cup (75 mL) rice beverage, eggs, coconut oil, vanilla and the cooked quinoa in a food processor. Pulse until very smooth.
Add quinoa mixture to dry ingredients and blend. Spoon batter into prepared pan.
Bake cake on middle rack of oven 65 min., or until centre of cake springs back when pressed. Remove from oven, cool cake in pan. Cover cake and keep at room temperature until ready to serve.
To serve, remove the springform pan's outer ring. Slice cake and plate. Garnish, if desired, with berries or other fruit.