Preheat your oven to 350°F (175°C).
Grease an 8x8-inch baking dish or a similar-sized ovenproof dish.
In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt.
In another bowl, mix the plant-based milk, orange juice, vegetable oil, orange zest, and vanilla extract until smooth.
Add the wet ingredients to the dry ingredients, mixing until just combined.
Pour the batter into the prepared baking dish and spread it evenly.