Grease a 1.2L pudding basin with reduced-fat spread. Cut a circle of non-stick baking paper to fit into the bottom of the dish. Spoon the agave syrup on top, and roughly spread out.
Add the flour, spread, sweetener, caster sugar, eggs, baking powder, vanilla extract, and ground ginger to a mixing bowl. 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.
Cover the basin and cook in the microwave for 6 minutes — until a knife inserted into the centre comes out clean. Leave to stand for 5 minutes.
Loosen round the edges of the basin with a knife, and place a plate on top. Flip over onto the serving plate, then slice and serve.