In a large mixing bowl, combine 250 grams of all-purpose flour (maida), 1/2 teaspoon of salt, 1/2 teaspoon of sugar, 1/2 teaspoon of baking powder, and 2 tablespoons of oil. Mix well.
Gradually add 100 ml of lukewarm water to the flour mixture and knead it into a soft dough. Cover the dough with a damp cloth and let it rest for 30 minutes.
Meanwhile, prepare the onion filling by finely chopping 2 large onions. In a bowl, mix the chopped onions with 1/2 teaspoon of salt, 1/2 teaspoon of red chili powder, 1/2 teaspoon of garam masala, 1/4 teaspoon of ajwain (carom seeds), and 2 tablespoons of chopped coriander leaves.
After the dough has rested, divide it into 6 equal portions. Roll each portion into a ball and flatten it slightly.
Place a portion of the onion filling in the center of each flattened dough ball. Bring the edges together and seal the filling inside. Gently flatten the stuffed dough ball again.
Heat a tawa or non-stick pan over medium heat. Roll out the stuffed dough ball into a 6-inch circle, taking care not to let the filling spill out.
Place the rolled-out kulcha on the hot tawa and cook for 1-2 minutes on each side, or until golden brown spots appear. Apply some ghee or butter on both sides while cooking.
Serve the onion kulchas hot with your choice of curry, yogurt, or pickle.