Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line a 9-inch square baking pan with parchment/baking paper.

Combine the strawberries, sugar, lemon juice and vanilla in a large saucepan, and cook over medium heat, stirring occasionally, until the strawberries have softened and released their juices, about 3-4 minutes.

Remove the strawberries from the heat. In a small bowl, mix the cornstarch and water to create a cornstarch slurry. Add to the strawberries and stir well to combine. Return to heat and cook for about 1 minute, stirring constantly, until thickened. Pour into a bowl and set aside to cool completely.

In a large bowl, mix sugar and lemon zest, rubbing the zest into the sugar with your fingertips. Add softened butter and vanilla, mixing until combined.

In a separate bowl, whisk together the gluten free flour blend, almond flour, xanthan gum, and salt. Add to the butter-sugar mixture and mix until it starts clumping together. Knead until you get a homogeneous cookie dough. Set aside.

In a large bowl, mix sugar and lemon zest, rubbing the zest into the sugar. Add softened butter, oil, and vanilla, and cream together until pale and fluffy.

Add the eggs, one at a time, mixing well after each addition.

In a separate bowl, whisk together the gluten free flour blend, almond flour, baking powder, baking soda, xanthan gum, and salt. Add half of the dry ingredients to the butter-sugar mixture, whisk well. Add yoghurt and whisk until smooth. Finally, add the rest of the dry ingredients and whisk until smooth.

Transfer the lemon cake batter into the lined baking pan and smooth into an even layer. Spoon the cooled strawberry filling over the batter.

Crumble the streusel topping over the strawberry layer.

Bake at 350ºF (180ºC) for about 40-45 minutes or until the crumble topping is evenly golden brown and an inserted toothpick comes out clean.

Allow the cake to cool until warm before removing it from the baking pan. Serve warm or cooled completely.