Rinse and drain the quinoa. Bring water and quinoa to a boil in a saucepan over high heat, stirring occasionally. Reduce heat, cover, and simmer for 15 minutes. Remove from the heat.

Blend together the milk, bananas, sugar, and salt in the bowl of a blender or food processor until smooth. Pour the milk mixture into the saucepan with the quinoa.

Place the pan over medium heat. Cook and stir until the mixture becomes thick and creamy, 5 to 10 minutes. Remove from the heat. Stir in the butter and vanilla and serve warm.