1. Preheat the oven to 350°F. Lightly spray a 9-inch circle cake pan, or an 8x8 inch baking dish with non-stick spray and set aside.
2. In a large bowl, whisk together the oats, flour, baking powder, cinnamon and salt. Add the raspberries and toss to coat them in the flour mixture.
3. In another bowl, mash the bananas and whisk them together with the brown sugar, egg, vanilla and milk until smooth.
4. Add this mixture to the dry ingredients and stir to combine.
5. Spread the batter in the prepared baking dish and bake for 30-35 minutes or until the edges are golden and a toothpick inserted in the center comes out clean.
6. Allow to cool for 5-10 minutes. While the cake cools, prepare the glaze.

For the Glaze:

1. Melt the butter in a small saucepan over medium heat and whisk in the powdered sugar.
2. Remove from the heat and whisk in the vanilla and milk until smooth.
3. Drizzle the glaze over the cake and serve warm.