IndianFoodForever provides a good basic chaat recipe for ragada patties. I'd add more tomato and make them very finely diced.
For the Patties (can be done ahead):
3 Potato (Aloo)
1/4 tblsp Coriander Leaves (Dhania Patta)
1/2 tblsp Garam Masala
1/4 tblsp Cumin Seed (Jeera)
1/4 tblsp Turmeric (Haldi)
Bread crumbs
Oil
* Boil, peel and mash the potatoes well.
* Take the mashed potatoes into a bowl, add ginger garlic paste, dhania powder, jeera powder, turmeric powder and salt.