Spray two 5" cake pans with cooking spray. Cut two circles to fit in the bottom of each, and spray those with cooing spray too. Set aside.
Preheat oven to 350 F.
Mix the coconut oil and pumpkin together until well combined in a large mixing bowl or stand mixer.
Add in the egg, applesauce, honey, and peanut butter. Stir or beat til combined.
Stir or beat in the flour and baking soda until all ingredients are wet. Fold in the 1 tablespoon of rainbow sprinkles.
Divide the batter between the two cake pans and smooth out the tops. Bake for 15 minutes or until an inserted knife comes out clean.
Let the cakes cool. You can put them in an airtight container for up to two days.
Once ready to ice, use a serrated knife to cut the domed part off the cakes. Set aside.
You can use the domed pieces to make a third layer for the cake if you want, or feed them to the dog as treats later. Either way, place the first layer on a cake stand or plate.
Use an offset spatula to ice the top of the first layer with the Greek yogurt.
Once iced, place the next layer on, and repeat until you've iced the top layer of the cake. Use the spatula to smooth yogurt icing in between the layers to make the signature Milk Bar cake look.
Top the cake with sprinkles as desired and serve immediately... outside in the yard!