Slice bananas and place in a large bowl. Add sugars, melted butter, water, lemon juice, vanilla, spices, and salt. Gently toss and let rest for 15–20 minutes.
Preheat oven to 375°F (190°C) and grease a 9×13-inch baking dish.
In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, whisk buttermilk, melted butter, and vanilla extract.
Add wet ingredients to dry ingredients and stir just until combined.
Pour banana mixture into the prepared baking dish. Gently pour topping batter over the bananas and sprinkle with turbinado sugar if desired.
Bake for 35–45 minutes until golden and set.
Cool for 15–20 minutes before serving with whipped cream or vanilla ice cream.