In a large bowl, sieve gram flour to remove any lumps. Add semolina, ginger-green chilli paste, turmeric powder, lemon juice, sugar, and salt to it. Slowly add water and whisk until you get a smooth, lump-free batter. Let it rest for 15-20 minutes.
Once the water is boiling and the steamer is ready, add Eno or baking soda to the batter. Mix quickly. You will see bubbles forming, which will make the dhokla fluffy. Do not over-mix, just stir enough to activate.
Immediately pour the batter into the greased tray and place it in the steamer. Steam on medium heat for 15-20 minutes. Once done, remove the tray from the steamer and let it cool slightly.
Heat 2 tablespoons of oil in a small pan. Add mustard seeds and let them crackle. Add sesame seeds, green chillies, curry leaves and a pinch of asafoetida. After a few seconds, add sugar, lemon juice and 2 tablespoons of water.
Pour the tempering evenly over the steamed dhokla. Garnish the dhokla with freshly grated coconut and chopped coriander leaves. Cut the khaman dhokla into square or diamond-shaped pieces and serve with green chutney or tamarind chutney.