Sift together the first 6 ingredients in a bowl.
In a stand mixer, add the butter, coconut oil, eggs, vanilla extract, stevia and yogurt and blend until well combined.
Skip this step if you don't mind seeing pieces of zucchini in the cake.Place the shredded zucchini into blender and blend until smooth like a thick soup.
While the mixer is on low gradually pour the zucchini into the egg mixture until incorporated.
Keep the mixer on low and in two batches slowly pour in the flour mixture.
It will be very thick so you may need to stop and scrap down the sides of the mixer bowl to continue to incorporate flour.
Grease the bottom and sides of a crock pot with coconut oil, butter or nonstick cooking spray.
Spread the batter into the crock pot and level off the top with a wet spatula.
If you are using the optional chocolate or carob chips, sprinkle those onto the top now.
Cover and cook on low 4-5 hours or until a toothpick in center comes out clean.
Uncover, turn off and allow to cool in the crock pot for 30 minutes before slicing and serving.
Loosen around the edges of the cake before slicing.