Preheat oven to 350F. Grease 3 donut pans and set aside.
In a large bowl, whisk oil, sugar, eggs, yogurt, milk, and vanilla until smooth.
In a separate medium bowl, combine flour, cocoa powder, baking powder, and salt. Fold flour mixture into liquid mixture until batter is just combined.
Scrape batter into a sealable bag and seal bag. Snip a corner off of the bag and pipe batter into prepared donut pan, filling each cavity about 3/4 full.
Bake donuts at 350F 10-12 minutes until donuts spring back when lightly touched. Allow donuts to cool in pan 10 minutes then transfer to a wire cooling rack.