Wash and peel the onions, dice them small. In a mortar, pound the onion until it is partly a paste then scrape into a bowl.
In a wide bowl, sift the flour, baking soda, and salt together, then add the pounded onion.
Mix everything together and then slowly add water and knead to a stiff dough.
Continue kneading well till the dough is soft and well kneaded.
Cover with a cloth and rest for half an hour.
When ready to cook the chapatis, heat a tawa, grease with cooking oil, and simmer.
Divide the dough into small orange sized balls. Dust well and using a rolling pin, roll out as discs.
When the frying pan is hot, place these discs on the griddle and cook. After a couple of minutes, when you find the bubbles coming up, flip to the other side and cook again.
Apply cooking oil / ghee on both sides and cook till golden brown on both sides.
Serve with side dish hot.