Set up a steamer by placing a rack or ramekin inside a large pot or Dutch oven. Add enough water to reach just below the top of the rack, bring to a boil, then reduce the heat to a gentle simmer and cover.

Lightly grease an 8-inch round cake pan with oil.

Whisk the besan, ginger, turmeric, salt, water, and lemon juice in a large bowl until a thin, smooth batter forms.

Vigorously whisk the fruit salt into the batter just before you are ready to steam until barely combined — the batter will foam up immediately.

Pour the batter into the prepared pan and gently smooth the top with a spoon. Avoid tapping the pan on the counter so you do not lose the air bubbles created by the leavening.

Place the pan onto the rack in the steamer, cover, and steam until a toothpick inserted into the center comes out clean, about 20 to 25 minutes.

Remove the pan from the heat and let the cake rest for 10 minutes.

Prepare the tempering by heating oil in a small saucepan over medium-high heat. Add the mustard seeds and cook until they begin to pop, then stir in the asafetida and remove from the heat.

Stir in the curry leaves and green chili until fragrant, then add the water and sugar, stirring until the sugar has completely dissolved.

Cut the cooled cake into 2-inch squares while still in the pan. Pour the warm tempering liquid evenly over the top and let it sit for 15 minutes to absorb the moisture.

Serve at room temperature with green chutney, topped with cilantro and coconut.