Prepare the Caramelized Raspberry Layer:

1. Preheat your oven to 350°F (175°C).
2. Grease a 9-inch round cake pan and line the bottom with parchment paper.
3. In a small bowl, mix the light brown sugar and melted coconut oil.
4. Spread the sugar mixture evenly on the bottom of the prepared cake pan.
5. Arrange the raspberries in a single layer over the sugar mixture.

Prepare the Lemon Poppyseed Sponge:

1. In a large bowl, whisk together the flour, granulated sugar, poppy seeds, baking powder, baking soda, and salt.
2. In another bowl, mix the mashed bananas, dairy-free yogurt, buttermilk, melted coconut oil, lemon zest, and vanilla extract until smooth.
3. Add the wet ingredients to the dry ingredients, mixing until just combined.
4. Pour the batter over the raspberry layer in the cake pan, spreading it evenly.

Bake the Cake:

1. Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
2. Allow the cake to cool in the pan for 15 minutes.

Invert and Serve:

1. Run a knife around the edges of the cake to loosen it.
2. Place a serving plate over the cake pan and carefully invert the cake onto the plate.
3. Remove the pan and parchment paper.
4. Dust with powdered sugar before serving.