Preheat the oven to 375F. Lightly oil a pie pan or line an 8-inch square baking dish with parchment paper or use a silicone baking pan.
Mix the ground flax seeds with the warm water and set aside to thicken.
Mix the turbinado sugar and cinnamon together in a small bowl. Set aside.
Combine the soy yogurt, soymilk, vanilla, and agave nectar in a bowl. Add the flax mixture.
Combine the flour, baking powder, and salt. Pour the soy yogurt mixture into the flour mixture and stir just until combined. Pour half of the batter into the prepared pan and spread to cover the bottom. Slice the bananas and place the slices over the batter. Sprinkle with half of the cinnamon-sugar. Spread the remaining batter over the bananas. Sprinkle with the remaining cinnamon-sugar. Bake for 25 minutes, or until cake appears set in the middle. Allow to cool for a few minutes before cutting into 6 slices and serving.