Preheat oven to 180°C (160°C fan-forced). Grease a 22cm springform pan with cooking oil and line the base with baking paper.
Heat the dairy free milk in the microwave for 30 seconds until warm (not boiling). Add the chai tea bags and let steep while preparing the batter.
Make the crumble topping. In a small bowl, mix the flour, brown sugar, and chai spice. Add the dairy free butter and rub it in using your fingers or a fork until the mixture resembles coarse crumbs. Place in the freezer to chill while making the cake.
In a large mixing bowl, beat the dairy free butter and white sugar using an electric mixer until light and fluffy. Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Remove the chai tea bags from the cooled milk, and squeeze the bags to release all remaining milk.
Sift the flour, baking powder, and chai spice mix into the bowl. Gradually add the milk to the bowl and continue to mix until the batter is smooth and creamy.
Pour the batter into the prepared cake pan and spread evenly. Sprinkle the chilled crumble topping over the batter.
Bake for 45 minutes, or until a skewer inserted in the centre comes out clean. Let the cake cool in the pan for 10–15 minutes, then release from the springform pan and transfer to a wire rack to cool completely.
In a small bowl, make the glaze by mixing the icing sugar, chai spice mix, and warm water (adding a little at a time) until smooth and pourable but not too thin.
Drizzle the chai glaze over the cooled cake, slice, and enjoy!