Preheat the oven to 375F. Grease and flour an 8 x 8 or 9 x 9 inch square baking pan.
To make the crumble topping, mix the flour, sugar, salt, and cinnamon in a mixing bowl. Add the butter. Use a pastry cutter or your hands to incorporate the butter into the flour, until the butter is the size of peas. Place the topping in the fridge while you make the cake.
To make the cake, whisk together the flour, sugar, baking powder, baking soda, salt, and lemon zest in a large mixing bowl. In another bowl, whisk together the non-dairy milk and vinegar. Stir in the oil and vanilla. Add these wet ingredients to the dry ingredients and stir until they’re just combined.
Pour the batter into the prepared baking pan. Distribute the blueberries on top of the batter, then sprinkle the crumble topping over the blueberries. Transfer to the oven and bake for 40-45 minutes, or until the cake is golden and the crumble topping is browning. Allow the cake to cool for at least 1 hour in the pan before cutting and serving.
Inspired by Cory Schreiber and Julie Richardson's Rustic Fruit Desserts.