Add rice and lentils to a large pot and rinse well a few times. Drain the water. Soak it in enough water for 3 to 4 hours.
Drain the water and add the rice, lentils, plain yogurt/curd and ½ cup to a grinder jar.
Blend to a smooth yet slightly coarse and thick batter (idli batter consistency). Add more water carefully if required, we want a thick batter.
Cover and ferment overnight or skip the fermentation to use baking soda or eno.
When you are ready to make the handvo, grate the vegetables and chop the greens. If you want to bake, preheat the oven to 180°C (350°F) for at least 15 mins.
Add the vegetables, salt, turmeric, ginger paste, hing, green chili, red chili powder and sugar to the batter. Stir well. Taste test and adjust the seasonings.
Pour oil to a 6 or 7 inch skillet and heat it on a low heat. Add mustard and jeera seeds. When they splutter, add curry leaves. Fry until they turn crisp.
Add the sesame seeds and spread them well all over the pan. (If you intend to bake then set aside half of the tempering.)
While you perform the above step, add baking soda to the batter and pour lemon juice over it. The mixture will get frothy. Mix it well with the batter.
Pour the batter to the hot skillet as much as you want. Gently spread the top evenly. (for baking, sprinkle the tempering we set aside all over on the top)
To bake in oven: Turn off the stove and transfer the skillet to the oven and bake for 35 to 45 minutes until a tester inserted comes out clean. The baking time depends on the pan size. For a 6 to 7 inch skillet it takes 35 to 40 mins. For the top golden crust you may broil for 2 mins.
Stovetop: Cover and cook on a low heat, until the top layer becomes almost dry and the bottom layer turns golden brown. This takes about 5 to 7 mins, flip it gently. The cook time depends on how much batter you pour and the size of your pan.
Cook the other side until crisp and golden. Flip again and cook on a medium heat until crusty.
Repeat with the remaining batter to make handvo.
Remove the handvo to a wired rack and cool before cutting it. Serve with chutney or any sauce.