Using a mandoline slicer, slice the onion into 1/8 inch thickness. You can also use a knife. Once that's done, put a pan on stove-top and add the following: white vinegar, water, sugar and salt.
Give it all a stir and heat on medium heat until the sugar dissolves then remove pan from heat. You don't need to boil it.
Add the sliced onions to a mason jar and then pour the prepared vinegar mixture over it. Stir and refrigerate for a few hours. It might look like that the vinegar is less to soak up all the onions but eventually the onions shrink in size and it's all submerged below the vinegar mixture. I sometimes invert the mason jar while it's in the fridge so that the onions on top also submerge in the vinegar.
Make the kathi rolls
To a small bowl add chole masala, coriander powder, Kashmiri red chili powder and garam masala. Then add 3 tablespoons water to the bowl and stir to make a paste with the spices. We add water so that the spices don't burn when we add them to the pan. Set this aside.
To a pan on medium heat, add 1 tablespoon ghee. Let it melt and then add ajwain. Stir few seconds and then add ginger juliennes and sliced green chili. Cook for 30 seconds, we don't want to brown the ginger.
Add the prepared spice paste into the pan and stir. Cook the spices for 30 to 45 seconds.
Then add in the chickpeas and salt (to taste). Stir until all chickpeas are well coated with the spices. Cook for 1 minute. Add 1 to 2 tablespoons additional water at this point.
Add cilantro and cook the chickpeas for 2 more minutes, stirring often and crushing some of the chickpeas with the back of your spatula. The filling is now done. Set this aside.
Heat up a tawa/skillet on medium heat. Once hot, place the frozen paratha on it. I have used plain Kawan paratha here. Cook the paratha until it's cooked and golden brown, following the instructions on the package. Cook all the parathas similarly.
To assemble the kathi rolls, take one paratha and spread mint chutney all over it. Then add the prepared chana masala in the center of the paratha. Top with some pickled onions and chopped cilantro.
Fold over from both sides to close the roll. You may use a toothpick to hold it in the center or wrap the roll in aluminum foil. Make all the rolls in the same way. Enjoy with more chutney on the side.
Notes
Do not replace ghee in this recipe. The flavor of this chana filling depends a lot on ghee. We are not using any onions or tomatoes here so ghee adds a lot of flavor.
To make this vegan, use vegan butter in place of ghee. I would not suggest using a flavorless oil here.
If you want to make these chana kathi roll gluten-free, you can use gluten-free wraps and follow rest of the recipe as is.
Leftover chana filling can be used in sandwiches or eaten with rice and dal or roti.
Chole masala is a blend of spices that you can find at any Indian grocery store. I use a local brand which I get from India but you can use any brand that's available at grocery stores like Everest etc.