Grease a 1.2 litre ovenproof pudding basin really well with reduced-fat spread. Cut out an 8cm disc of non-stick baking paper. Grease the disc of paper and place, greased side up, in the bottom of the pudding basin.
Place the flour, reduced-fat spread, white granulated sweetener, caster sugar, cocoa powder, eggs, baking powder and vanilla extract in a medium bowl. Beat with an electric whisk for 1-2 minutes on high speed, until you have a smooth cake batter. You can use a wooden spoon, but more effort will be needed.
Scrape the mixture into the prepared pudding basin using a rubber spatula. Level the surface if needed and loosely cover, leaving a small gap at the edge.
Microwave on high for 4 ½-5 minutes. The pudding will be ready when risen, spongy and a knife inserted into the centre comes out clean. Leave to stand for 4-5 minutes, remove the covering and run a round bladed knife around the edge to loosen the pudding.
Turn out onto a serving plate, taking care as the pudding will be very hot. Spread the low-calorie chocolate syrup over the top of the hot pudding and allow it to melt and run down the sides.
Serve hot, alone, or with Custard or Chocolate Custard.