Preheat the oven to 350 degrees. Line a 9x9 pan with parchment paper.
Place the sliced berries into a large bowl. Combine the brown sugar and cornstarch and pour over the berries. Stir gently to coat the berries with the sugar. Set aside to rest while you mix the cake.
In a large bowl, combine the flour, sugar, brown sugar, baking soda, baking powder, cinnamon and salt. Mix well and set aside.
In a second bowl, whisk the eggs until frothy.
Add the melted coconut oil and vanilla to the eggs. Whisk until smooth.
Add the egg mixture and the mashed banana to the dry ingredients. Fold together with a spatula until the flour is incorporated.
Line the bottom of the pan with your sugared strawberries. Do not pour the liquid into the pan.
Spoon the cake batter on top of the berries, so as not to disturb your pattern.
Gently spread the batter around on top of the strawberries using an offset spatula.
Bake in preheated oven for 30-35 minutes, until top springs back when gently poked.
Remove and cool in pan for 10 minutes, then gently flip over onto a cooling rack to cool completely.
Store leftovers in an airtight container in the refrigerator.