Soak dal and rice for at least 4 hours or preferably overnight.
Grind the dal and rice mixture. Make sure to grind well. You want the mixture to be very smooth. Add salt. Pour the batter into a large bowl, cover and leave it in a warm place to ferment. If it is winter, keep near a heater or in the oven (turned off).
When you are ready to make uttappams, take out some batter in a separate bowl. Take a small pinch of soda bicarb, add to ½ teaspoon water and mix in the batter. This makes the uttappams very fluffy.
Heat 1 teaspoon oil on a tawa. Add a one or two ladles of batter on top and spread into a circle. Cover with a lid and let cook for a few minutes till set. Now sprinkle the onion, green chillies, carrots, and coriander leaves on top. Add some oil and flip over gently. Let it cook for a few minutes on the other side. Flip back (topping side up) on a plate. Garnish with some fresh coconut and serve.