In a bowl mix the semolina, oats flour, grated ginger and salt.
Add the yogurt and whisk well to combine. Add upto 3-4 tbsp of water to make a smooth but thick batter, with the consistency of idli batter. Mix in juice of half a lemon.
Add Eno fruit salt, and add 1 tsp of warm water over that. Whisk well until the batter is light and frothy.
Grease a 6-7 inch dish with a rim, that will fit easily into a steamer with a lid. Place the dish inside the steamer with water, and allow the water to come to a boil.
Pour the frothy batter into the greased plate and close the steamer lid. Steam for 12-15 minutes.
Meanwhile, heat the oil in a small pan. Add the mustard seeds and sesame seeds, once the mustard splutters, the tempering is ready.
Once cooled, remove the dish from the steamer. Allow this to cool for 5 minutes. Cut into squares or diamond shapes with a sharp knife.
Transfer the tempering over the dhokla pieces and serve hot with green chutney.