1.Adding zest elevates the taste but if you don't have zester, just leave it. Do not use cheese grater or carrot grater to grate the skin as it will scrape out the white part and make the cake bitter.
2.You shall skip Jaggery caramel and directly add powdered jaggery or cane sugar to egg mix. Caramel enhances the color and flavor of the cake though.
3.You shall skip eggs and add ⅓ cup milk. Warm the milk, add 1 tsp lemon juice to curdle it. Cool down and then add it to the wet mix.
4.You shall skip oil and add butter. If using butter, keep ½ cup butter out in room temperature until it becomes soft. In wet mix, first beat the butter until creamy, then add ½ cup powdered jaggery or cane sugar and beat well until creamy. Then add one egg and beat well. Then add the other egg and beat well. If adding butter, then ½ cup jaggery or sugar is required as butter will curdle if egg is directly added to the butter without sugar/jaggery. So, if adding butter and egg, you need to add more sweetener, as mentioned. If you want to lessen the sweetness, then you shall add butter(whisk until creamy) but skip egg and add curdled milk as mentioned in the last point.
5.Coconut oil doesn't impart coconut oil flavor to the cake and I prefer coconut oil. You shall replace it with any neutral-smelling cooking oil.