You can fill the puri up with anything, and top it with anything.
Here’s what to do for a typical sev puri chaat:
puris, which can be bought at any Indian store, or you can make your own
1 potato, peeled, boiled, diced, for filling
red onion, diced, for filling
tomato, diced, for filling
tamarind chutney, for topping
green chutney, for topping
yogurt, beaten, for topping, leave out if vegan
sev, for topping, which can be bought at Indian store
chopped cilantro, for topping
red chili powder, for sprinkling
chaat masala powder, for sprinkling
Tap a hole into each puri and stuff it with the filling ingredients. Then top the puris with the topping ingredients. So easy, yet so delicious! Most people pile on the sev, but I like just a subtle amount. Do what you want!