Wash and soak the chana dal in sufficient water overnight.
In a bowl, mix the udad dal flour and rice flour. Add 1/2 cup water and mix well to make a thick batter. Cover and ferment overnight.
Drain the soaked chana dal and grind along with grated ginger to a coarse paste using 1/4 cup water.
Add the fermented rice-udad dal batter and the chana dal paste to a bowl. Add turmeric powder. Grate the cucumber (with skin) and carrot into this. Season with salt. Mix in 1 teaspoon of oil and the lemon juice.
Grease the idli plates with 1 tsp oil. Place 1-2 cups of water inside the pressure cooker / idli steamer and cover. Let the water come to a boil, and the steam to build up.
Meanwhile, add Eno fruit salt to the batter, top with 2-3 tbsp of hot water and mix it up well to get a fluffy batter. Pour ladleful of the batter in each idli mould.
Open the lid of the steamer, place the idli stand and steam for 8-9 minutes.
Remove and allow to cool for 5 minutes, before unmolding the idlis with a sharp edged spoon.
Serve with chutney / molaga podi and with a glass of Buttermilk.