It's best to approach street-side dining in Mumbai—or anywhere in India, for that matter—with caution. But caution, if you love Indian food, is torture. While working in Mumbai, and studying the city's culinary specialties, I learned that you don't typically go to restaurants for great food, you go to the sidewalks. My daily commute took me past hawkers selling the food I craved: pav bhaji, a vegetarian sloppy joe made with tomato and potato stew; pani puri, hollow fried balls stuffed with spicy potatoes or chickpeas; and the dish I crave to this day, vada pav.

The...