Preheat the oven to 350°F. Lightly grease a 8" square baking pan.
In a mixing bowl, combine oat milk, lemon juice and set aside for 5 minutes to curdle. Stir in the oil, sugar, vanilla and orange/ lemon extract. Whisk until smooth.
Sift in the flour, cornstarch, baking powder, baking soda and salt. Gently mix to just combine all the ingredients. Make sure not to overmix, small lumps are OK.
Pour the batter into the prepared baking pan. Bake for 30~32 minutes or until a cake tester inserted into the center comes out clean.
Remove the cake from the oven and let cool for 1~2 minutes, then poke holes using a toothpick at about ½" intervals.