Heat the ghee (or oil) in a heavy, nonstick saucepan over moderate heat.
Once shimmering, add the green chilies and cumin seeds.
Fry for about 30 seconds, until the seeds begin to crackle and darken.
Stir in the cubed zucchini, turmeric, ground coriander, fresh peas (if using), and half of the fresh coriander. If you used vegetable oil, add the butter now.
Stir well to coat.
Cover the saucepan and cook for 10 minutes, stirring occasionally. The zucchini will release its own water, so there's no need to add any.
Uncover and continue to sauté for another 2-3 minutes, allowing any excess liquid to evaporate and the squash to become perfectly tender.
If using frozen peas, stir them in now and cook for 1-2 minutes until heated through.
Remove from heat.
Stir in the salt and the remaining fresh coriander. Gently mix and serve immediately.