Preheat oven to 350°(F).
Cut out three 9-inch round segments of parchment paper to line your cake pans with. Spray each pan generously - sides and bottom - with nonstick baking spray, then place the parchment paper cut out in the bottom of the pans and spray again. It's important to make sure every bit of pan and paper are sprayed so your cakes don't get stuck.
Set pans aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, combine both sugars, flour, cocoa powder, baking soda, baking powder, salt, and cinnamon; mix on low speed until dry ingredients are thoroughly combined.
Use your hands to break up any large clumps, if needed.
In a separate bowl combine the eggs, egg yolks, zucchini, Greek yogurt, oil and vanilla extract; mix until completely combined.
Pour mixture into the dry ingredients and beat on low until just incorporated. Pour in hot water and continue mixing until completely combined; about 1 minute. The batter will be thin.
Divide batter evenly among prepared pans. Bake in preheated oven for 30 minutes, or until a wooden toothpick or cake tester inserted in the center of a cake comes out clean or with just a few moist crumbs attached.
Cool cakes for 10 minutes in the pans before removing from pans and transferring to a cooling rack. Cool cakes completely before frosting. *If you don't have enough room to bake all 3 cakes on the same rack in an even line, bake 2 at a time.