Preheat your oven to 350F / 175C. Then take out your 8" bundt pan (see directions for other types of cake pans above), brush every surface with a little oil, and then dust it with flour.
Put the vegetable oil, 3/4 cup of non-dairy milk, vanilla extract, sugar, baking powder, salt and orange juice into a large bowl. Mix until well combined.
Add flour and stir until incorporated.
Divide your cake batter into two bowls. Add cacao powder and 1tbsp of non-dairy milk to one half. Stir to combine.
Add orange zest to the other half and stir to combine.
Pour a little bit of your chocolate mixture into the pre-prepared bundt pan, followed by a little of the orange mixture. Repeat this step until you have no more cake batter left in your bowls.
Bake the cake for 45-50 minutes, until a toothpick can be inserted and come out clean. Let the cake cool before taking it out of the bundt pan.
Optional: sprinkle powdered sugar on top of the cake before serving.
Notes
Store any leftovers in an airtight container for up to 5 days.