Preheat oven to 350˚F. Line an 8-inch square pan with parchment and leave some hanging over the sides.
Place the bananas, eggs, melted butter, vanilla, syrup, and sugar into a food processor. Pulse until fully puréed.
Pour mixture into a large mixing bowl.
Add the quinoa, quinoa flakes, chia seeds, salt, and baking powder.
Gently fold mixture to combine, then pour into baking pan.
Bake just until the cake is firm through to the center (30 minutes). Remove and allow to fully cool. Lift cake from pan by the parchment and cut into squares.
Microwave the chocolate on defrost in 30-second increments, stirring in between, until fully melted.
Stir softened butter into the chocolate.
Pour mixture into a zip-top bag, snip a small hole in the corner and pipe chocolate onto each square in a crosshatch pattern.
Allow chocolate to set for 5-10 minutes before serving.
