Grease a 9" or so microwave safe flatware with some ghee on your fingertips. Keep aside.
In a blender / mixer, place the 3 peeled bananas with the jaggery, make a smooth paste and keep aside.
Heat the remaining ghee in a heavy bottomed wok, put in the semolina. On medium to low flame, constantly stir it around until it turns lightly golden. This part requires your full attention for 5-7 minutes and the slightest burnt semolina will spoil the taste of the cake.
Once the semolina turns golden, turn flame to lowest possible, pour in the banana-jaggery paste, stir till it is nearly absorbed by the semolina. This will take 30 seconds to a minute. Take the wok off the flame.
In a jug, whisk well the coconut milk, water, salt, baking powder, cardamom powder and pour it into the semolina mix in the wok. Stir well till ingredients are blended through.
Pour this mix into the greased microwave safe dish. Garnish with any nuts /dried fruits or candied fruit to make it more appealing to kids.
Microwave at 100% for 5 minutes. Check the degree to which the cake is cooked and then depending on that microwave at 80% for 2 minutes or so. Remove, cool and cut into squares /diamonds.