1)You can adjust the sugar level as you like.
2) If you want to cover the entire cake, then double the quantity of chocolate for icing.
3) My oven's maximum temperature is 800 watt. And the cake was done in 4 mins. So keep a eye on your cake.
4)This cake wont rise much, But it will rise a little. So don't over fill the bowl. Fill it halfway through.
5)You could use melted butter for oil.
6)Grease the bowl well, so the cake doesn't stick to the pan.
7)Allow the cake to cool completely before inverting.
8)Use little sour curd, that will react with baking soda and make the cake spongy.