Rinse the quinoa: Place the quinoa in a fine-mesh strainer and rinse under cold water until the water runs clear. This removes the natural coating called saponin, which can make quinoa taste bitter.
Cook the quinoa: In a medium saucepan, combine the rinsed quinoa with 2 cups of water. Bring to a boil over medium-high heat, then reduce the heat to low, cover, and simmer for about 12-15 minutes, or until the quinoa grains have opened and the water is mostly absorbed. The quinoa should be tender but not mushy.
Add milk and oats: Once the quinoa is cooked, add the milk, oats, and stevia to the saucepan. Stir well to combine. Cook over low heat for another 3-5 minutes, stirring occasionally, until the mixture thickens slightly and the oats are soft.
Incorporate vanilla: Remove the saucepan from the heat and stir in the vanilla extract. Let the mixture sit for 2-3 minutes to allow the flavors to meld.
Serve or store: Divide the mixture into two bowls or meal-prep containers. If serving immediately, add your favorite toppings, such as fresh berries, sliced bananas, or a sprinkle of nuts. If meal prepping, let it cool completely before sealing and refrigerating.