In a large saucepan or bowl, combine the chopped fresh strawberries, granulated sugar, and lemon juice. Place the saucepan over medium heat and allow the mixture to bubble gently for 2 to 3 minutes.

Mix the all-purpose flour with 1 tablespoon of water to create a slurry, then stir it into the strawberry mixture. Continue cooking for another 1 to 2 minutes until it thickens. Remove from heat and set aside to cool completely.

In a small bowl, combine the all-purpose flour, granulated sugar, melted vegan butter, and ground cinnamon. Mix until crumbly and chill in the fridge.

Preheat your oven to 180°C (355°F). Line an 8-inch (20 cm) square baking pan with parchment paper.

In a large mixing bowl, whisk together the dry ingredients: flour, sugar, baking powder, and salt. Add the wet ingredients and whisk until combined, being careful not to overmix.

Pour the vanilla cake batter into the prepared pan. Spoon the cooled strawberry layer over the batter, then sprinkle the chilled crumb topping evenly on top.

Bake for 1 hour to 1 hour and 5 minutes.

Allow the cake to cool in the pan for about 30 minutes. Carefully lift the cake out and transfer to a wire rack to cool completely. Cut into 16 portions.