Preheat your oven to 350°F (175°C). This ensures your cake bakes evenly.
Grease a 9x13 inch baking pan with butter or cooking spray to prevent sticking.
In a large mixing bowl, whisk together the melted butter, eggs, milk, and vanilla extract until smooth and creamy.
Gradually add the white sugar to the wet mixture, whisking continuously until well combined.
In another bowl, sift together the cocoa powder, baking powder, baking soda, and salt. This helps to avoid any lumps and ensures even distribution.
Slowly add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.
Gently fold in the cooked quinoa and chocolate chips until evenly distributed throughout the batter.
Pour the cake batter into the prepared baking pan, spreading it evenly with a spatula.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 15 minutes before transferring it to a wire rack to cool completely. Once cool, spread the chocolate frosting generously on top.