Take a wide pan or Kadai and add the oil and butter to the pan. When the butter is melted add chopped onions to the pan.
When they are lightly fried add ginger garlic paste. Saute it until the raw flavor is gone.
Then add finely chopped capsicum to the pan. when the capsicum is slightly cooked add chopped tomato.
Cook the tomatoes until they become soft. Then add salt, chili powder, green chilis, pav bhaji masala and mix well.
Fry the spices along with the veggies. Then add boiled veggies to the pan and mix well with the spices in the pan. Add some water if required. Then add chopped coriander leaves and mix well.
Then mash the veggies with the potato masher or spatula. Don't paste the veggies, you should have chunks of veggies in the Bhaji.
After that add the lemon juice to the pan and mix well. When Bhaji is thick enough turn of the stove.