Pressure cook the veggies in 1 cup water for 3-4 whistles. Heat oil in pan and saute the onion till light brown.
Add the ginger-garlic paste, tomato paste and all the dry spices mixed with some water to form a paste. Saute till the oil separates.
Now add the tomatoes and fry on a low flame till well mashed. Add the boiled veggies and continue to simmer on low flame, simultaneously mashing it with a masher. When almost done, add a tsp. of butter and give it a mix.
Heat another tsp. of butter on a tawa / griddle and toast the pav halves on both sides. Serve the pav bhaji with a dollop of butter on top of it along with the toasted pavs, chopped onion, green chilies and lime wedges.
