Preheat the oven to 350 degrees. Spray an 8x8 cake pan with nonstick baking spray and set aside.
Add your eggs and sugar to a bowl and beat for 3 minutes.
Add the oil yogurt, vanilla, and espresso powder and mix to combine.
Add your dry ingredients and mix until just incorporated.
Add your coffee and stir to combine.
Pour batter into prepared cake pan. Bake for 35-45 minutes or until a toothpick comes out clean.
Allow to cool completely.
Add all of your ingredients for the buttercream to a bowl. Mix until creamy and fluffy. If the mixture seems a little too thick add an additional tablespoon of oat milk.
Pipe 1" stripes across the cake.
To make the ganache, place the ingredients in a microwave safe bowl. Microwave in 30 second intervals, stirring in between, until chocolate is fully melted and creamy.
Pour the chocolate ganache over the top of the cake and allow to cascade over the bumps.