Wash the cauliflower and remove the stem and leaves, while keeping the flower whole.
Fill a large pot (big enough for the cauliflower) halfway with water and bring it to a boil. Once the water starts boiling, carefully place the cauliflower and blanch for 5 minutes. Strain and let the cauliflower cool down a bit.
Mix together curds, a tablespoon of oil, both chili powders, turmeric powder, coriander powder, garam masala powder, chaat masala powder, ginger garlic paste and salt till blended.
Once the cauliflower is cool, rub the curds mixture all over the cauliflower, potatoes and onions. Let it sit for 10 minutes.
Pre-heat oven to 200 degrees celcius.
Brush an oven proof skillet or roasting pan large enough to fit the cauliflower with oil.
Place the cauliflower in the skillet along with onions and potatoes and brush with oil. Bake for 20 -25 minutes till the top is golden brown and the cauliflower is cooked through. (Half way through, brush once more with oil)
Squeeze lime juice and sprinkle coriander leaves on top. Serve immediately.