Take a medium or large tawa or pan and add 2 tbsp butter in it. Add 1 tsp cumin seeds, 2 chopped green chilies, 1 tbsp ginger garlic paste and saute till paste turns brown.
Add 1 chopped onion and saute till onion turns translucent and pink.
Then add 1/4 tsp turmeric powder and 1/2 tsp red chilli powder. Mix well.
Add 2 chopped tomatoes and 1 chopped capsicum. Mix.
Cook on moderate heat until tomatoes and capsicum turn soft and mushy.
Put 3 tbsp water in it.
Mash to get smooth paste like consistency.
Add 3 tbsp pav bhaji masala, 2 tsp lemon juice and cook till you get a dry but spreadable paste. There must not be too much moisture in it.
Put 2 tbsp coriander leaves and mix well.
Keep the masala aside using a spatula.
On the side of tawa or pan, put 1 tsp (for 2 pav) of butter. When butter melts, toss pavs after splitting them from the center.
In the middle of pavs, spread some masala.
Top with some chopped onion and coriander.
Put the top part of pav over the spread masala.
Serve with lemon wedges.