In a large bowl, combine the flour, salt, and sugar. Mix well.
Add the vegetable oil and rub it into the flour mixture until it resembles coarse crumbs.
Gradually add warm water, mixing until a soft dough forms.
Knead the dough on a floured surface for about 5 minutes until smooth.
Cover the dough with a damp cloth and let it rest for at least 30 minutes.

Drain the soaked yellow split peas and cook them in a pot with enough water to cover them. Bring to a boil, then simmer until the peas are tender (about 30-40 minutes). Drain any excess water.
In a pan, heat the vegetable oil over medium heat. Add the mustard seeds and cumin seeds. Once they start to crackle, add the chopped onion and green chili (if using). Cook until the onion is soft and translucent.
Add the cooked split peas, turmeric powder, and salt. Mix well and cook for another 5 minutes until the mixture is thick and dry. Set aside to cool.

Divide the dough into equal-sized balls (about 8-10).
Roll each ball into a small circle (about 4-5 inches in diameter) on a floured surface.
Place a spoonful of the split pea filling in the center of each dough circle.
Fold the edges of the dough over the filling to seal it, then flatten it gently with your hands or a rolling pin.
Roll out each filled dough ball into a thin circle (about 6-8 inches in diameter), being careful not to let the filling spill out.

Heat a griddle or non-stick pan over medium heat.
Place the rolled dholl puri onto the hot griddle. Cook for about 1-2 minutes on each side, or until brown spots appear and the dough is cooked through.
You can brush a little oil on the dholl puri while cooking if desired.

Serve hot with pickles, chutneys, or curry of your choice.
Enjoy your meal!