Preheat the oven to 350 degrees F and grease a 9-inch round baking pan.
Place the oats, coconut, cocoa powder, baking powder, salt, flaxseed, and chocolate chips into the bowl of a food processor. Grind into a coarse powder, about 30 seconds.
Add the yogurt, eggs, maple syrup, and vanilla and process for an additional 30 seconds. Pour batter into the prepared baking pan (the batter will be thin) and bake for 28-30 minutes or until a cake tester inserted into the center of the pan comes out cleanly. Cool for 5 minutes in the pan on a wire rack, then invert onto a wire rack out of the pan and let cool completely. Top with frosting and serve immediately, or cover and store in the fridge up to overnight before serving.
Serves 8-10 (or more if just for little ones!)