Preheat oven to 350°F (175°C). Grease a 9-inch pan.
In a large bowl, whisk together flour, baking powder, baking soda, and salt.
In another bowl, mix sugar, oil, almond milk, vanilla, and vinegar.
Add wet ingredients to dry ingredients and mix until combined.
For the streusel, combine sugar, flour, oats, cinnamon, and vegan butter. Mix until crumbly.
Pour batter into the pan, sprinkle streusel over the top.
Bake for 30-35 minutes or until a toothpick comes out clean.
Cool for 10 minutes, slice, and enjoy.