For the filling: In a wok or kadai add oil. When hot add mustard seeds and allow it to splutter. Now add split urid dal, jeera or cumin seeds, fennel seeds, and allow to saute for a couple of minutes.
Now add the finely chopped onions and garlic. Fry for a couple of minutes. Then add ginger paste.
Once the onions are soft and golden brown, add the smashed potatoes. To this add all the masala powders including garam masala powder and kalonji seeds.
Now add black salt and coriander leaves. When the potato pooran is well cooked for 5 to 10 minutes. Switch off the flame and add lemon juice.
Now for the poli. Make a soft pliable dough with the wheat flour and besan flour. Add black salt, and lukewarm water. Knead into a soft dough like you do for chapathi. Add oil.
Now make small cups of these wheat dough and put the potato filling. Then roll them into chapathis. Now cook them on sim flame. Spicy potato poli ie ready. Serve with tomato sauce.