This recipe has been adapted from "From Curries to Kebabs" by Madhur Jaffrey
Pour oil into a large saucepan or wok, and set over medium-high heat. When oil is hot, add asafetida, and in quick succession, cumin seeds and mustard seeds. As soon as mustard seeds begin to pop, add zucchini and green pepper. Cook, stirring, for 5 minutes. Add yogurt, and cook, stirring, until yogurt has been absorbed. Reduce heat to low, and add coriander, chaat masala, and salt. Cook, stirring, for 1 minute. Drizzle with lemon juice; toss to combine, and serve.