In a large pot, add the split peas and water. Bring to a boil and then reduce the heat to low. Simmer for about 30 minutes, or until the split peas are soft and cooked through.
Drain any excess water and mash the split peas until smooth.
In a skillet, heat the vegetable oil over medium heat. Add the chopped onion, garlic, and green chili (if using). Sauté until the onions are golden brown.
Stir in the turmeric, cumin, coriander, black pepper, and salt. Cook for another 1-2 minutes until fragrant.
Add the mashed split peas to the skillet and mix well. Cook for an additional 5 minutes, stirring occasionally. Remove from heat and let the filling cool.
In a large bowl, mix the flour, salt, and baking powder.
Add the vegetable oil and mix until the mixture resembles coarse crumbs.
Gradually add warm water, a little at a time, and knead to form a smooth and elastic dough. You may need more or less water depending on the flour.
Cover the dough with a damp cloth and let it rest for about 30 minutes.
Divide the dough into small balls (about the size of a golf ball).
On a lightly floured surface, roll out each ball into a small circle (about 6 inches in diameter).
Place a spoonful of the filling in the center of each dough circle.
Fold the edges of the dough over the filling to enclose it, pinching the edges to seal.
Gently roll out the filled dough ball into a flat disc, being careful not to let the filling escape.
Heat a tava or skillet over medium-high heat.
Place the rolled-out dhal puri onto the hot skillet and cook for about 2 minutes on each side, or until golden brown spots appear and the dough is cooked through.
Repeat with the remaining dhal puri.
Enjoy your meal!