IndianFoodForever provides a good basic chaat recipe for ragda patties. I'd add more tomato and make them very finely diced.

For the Patties (can be done ahead):
3 large Potatoes
1/2 tsp ginger, grated
1/2 tbsp Garam Masala
1/4 tbsp Turmeric
2 Tbsp Bread crumbs
Oil

Peel, quarter, and boil the potatoes until soft, then mash them or pass them through a ricer.
Add spices, mix and knead well into a dough.
Add the bread crumbs and knead well.
Divide the dough into golf-ball sized balls, press each ball with hand so that it would make into a round patty.
Heat oil and fry the prepared patties in the oil till golden brown on both sides.

For the stew/ragda:
1 tbsp Chaat Masala Powder
1/2 tbsp Ginger Garlic Paste
2 cups of cooked Chickpeas
4 tbsp Oil
1 Onion
1 can diced tomato
1/2 tbsp Garam Masala
1/4 tbsp Turmeric
1/2 tbsp Red chili powder

Heat oil, add chopped onions and sautee untill they are light golden brown.
Add ginger garlic paste, turmeric powder, garam masala powder, chat masala powder, red chilli powder and fry for 30 seconds.
Add tomatoes and salt, cover, and cook on medium heat for 3-5 minutes until the tomatoes are soft.
Add the chickpeas, 1 cup of stock or water, stir, cover and cook on medium heat for 3-4 minutes.

To serve:
Take the serving plate, put two cutlets in the plate.
Pour the ragda on the cutlets.
Sprinkle chopped onions and coriander leaves.
Sprinkle a pinch of chat masala powder and serve hot.
Serve with Indian chutneys.