Preheat the oven to 180C/350F/gas mark 4. Grease an approx 11.5 x 21.5 cm / 4.5 x 8.5 in loaf tin and line with a strip of baking parchment, leave some overhanging on either side so that you can easily lift the bread out once it is baked.
To make the streusel topping, mix the crushed Lotus Biscoff biscuits, melted vegan butter, plain flour, cinnamon and brown sugar in a small bowl. Set aside.
Whisk together the vegan butter and light brown soft sugar with an electric mixer until smooth and creamy.
Next, whisk in the mashed bananas, vanilla extract, cider vinegar and non dairy milk. The mixture will look a bit split and gross, don't worry!
In a separate bowl, sift together the plain and wholemeal flours, baking powder, bicarbonate of soda, cinnamon, nutmeg and salt
Tip the dry ingredients into the wet and whisk until just combined; be careful not to over-mix.
Pour half of the batter into the prepared tin and spread level. Dot over half of the Biscoff spread. If it is too firm then pop it in the microwave for a couple of seconds until it has softened slightly. Use a knife to gently swirl the biscoff through the batter; don't mix it in too much however.
Spread the other half of the batter over the top then dot over the rest of the biscoff and swirl in as before. Scatter over the streusel topping.
Bake for 60-70 minutes until a skewer inserted into the centre comes out clean or with a few moist crumbs. If the top starts to get too dark before the cake is cooked, loosely cover it with a piece of tin foil.
Allow to cool in the tin for about half an hour then use the overhanging parchment to lift the loaf out onto a wire rack to cool completely.