Soak rice and urad dal for 4~6 hours. Grind them to a smooth batter adding enough water. Cover and set aside to ferment for at least 8 hours or overnight.
When ready to make dosas, add oats powder, tomato puree, cumin seeds and salt to the dosa batter and mix well.
When ready, heat a tawa on medium high heat. Pour about ½cup of batter and spread it around using the back of a ladle. Add few drops of oil on the batter and let cook until lightly brown and crispy, about 2~3 minutes. Carefully flip and cook on the other side for 30 seconds. Remove and serve hot with potato curry (similar to this curry but without the besan) and/ or peanut or ginger chutney.