Grease a 1.2 litre pudding basin with reduced-fat spread. Cut a circle of non-stick baking paper to fit into the bottom of the dish. Then spoon the agave syrup on top.
Add the flour, spread, sweetener, caster sugar, eggs, baking powder, vanilla extract, and ground ginger to your mixing bowl. Then whisk with an electric whisk for 2 minutes — until light and creamy.
Scrape the cake mixture into the bowl, on top of the syrup layer.
Cut a 28cm circle of non-stick baking paper and tear off a section of foil, slightly bigger than the circle. Layer the paper, then foil, and wrap the top of the dish tightly — with the paper on the inside.
Place the pudding basin into the slow cooker pot and pour boiling water into the slow cooker, about halfway up the sides of the pudding basin.
Cook for 2.5-3 hours — until a knife inserted comes out clean. Remove the pot from the slow cooker. Then loosen around the edge of the pot with a knife, and place a plate on top. Flip over onto the serving plate, slice and serve.