Soak chana dal for 30 minutes. Then boil until very tender but not mushy. Drain and reserve the cooking liquid. Spread the cooked dal on a wide plate and let cool.
Once cool enough to handle, grind to a smooth powder along with cumin and salt. I added a pinch of red chili powder – it is not traditionally used. Set aside.
In a mixing bowl, combine the flours, salt and turmeric. Add the reserved dal cooking water and oil. Mix and knead until a soft, pliable dough forms. Add more water, if needed. Cover and set aside for 10 minutes.
Divide the dough into 12~15 equal size pieces. Flatten them out into a flat disc and make a depression in the middle. Fill the depression with generous amount of dal powder. Bring the dough ends over the filling encasing it. Flatten it again and roll into a roti – the thinner the better.
Place the stuffed roti on a preheated griddle or tawa and cook on medium-high flame until lightly golden on both sides. Brush with oil while cooking. Repeat with the remaining dough and dal filling.
Traditionally Dholl puri are made entirely with all purpose flour, so you can use 3 cups of APF and skip whole wheat flour.