Make the Puris:
In a bowl, mix semolina, all-purpose flour, and baking soda. Add water gradually to form a stiff dough. Cover and let it rest for 15 minutes. Roll out the dough thinly and cut into small circles using a cookie cutter. Heat oil in a deep pan and fry the circles until golden and puffed. Drain on paper towels. Prepare the Pani:
In a blender, combine mint leaves, coriander leaves, green chilies, ginger, tamarind pulp, and lemon juice. Blend to a smooth paste. Transfer to a bowl, add roasted cumin powder, black salt, sugar (if using), salt, and cold water. Mix well and refrigerate until ready to use. Prepare the Boondi Filling:
In a bowl, mix boondi, mashed potatoes, chickpeas, chaat masala, and salt. Assemble the Pani Puri:
Gently make a hole in the center of each puri.
Fill with the boondi mixture.
Dip each filled puri into the mint pani and serve immediately.