Preheat the oven to 180°C. Grease and line a loaf tin.
Melt the margarine and let it cool.
Mash the bananas in a small bowl.
In another bowl mix the oaty milk, oats and sultanas together.
Sift together the flour, cinnamon, mixed spice and baking powder in a large bowl.
In another bowl whisk the sugar and eggs until creamy, then add this to the flour mixture. Stir, then add the bananas and the soaked oats and sultanas.
Transfer the batter into the tin, allowing to spread out evenly.
Bake for 50-60 minutes, until an inserted skewer comes out clean.
When the cake is ready, take it out of the oven and let it cool for 5 minutes in the tin, then transfer it to a wire rack.
Let it cool completely, then slice.