Heat oil in a sauté pan; add mustard seeds and cumin seeds; once the seeds start to splutter; add curry leaves, onion and green chilies; sauté until onion is translucent, about 5 minutes.
Now add snake gourd and ½ cup water; cover and cook till it turns tender, about 8-10 minutes. Season with salt.
Then add tomatoes; cover and cook till they turn mushy, takes another 5 minutes.
Add the roasted sesame powder, red chili powder and salt; cook for a minute.
Whisk rice flour into milk and add it to the curry; mix well and simmer for 2-3 minutes. Enjoy with rice or roti.