Take a pan heat some oil, saute chopped onions till golden brown, add green chillies and ginger saute it for 2-3 minutes. Now add turmeric, red chilli, pav bhaji masala(1 tsp), tomato cook it for 3-4 minutes and add all the vegetables.
Using a spatula, simultaneously mash and stir all the vegetables. Add about ¼ cup of water or as needed. Cook till everything thoroughly cooked.
Add remaining pav bhaji masala, coriander and lemon juice(as per taste) and mix it well.
Toast the halves bun over a skillet using butter over medium heat until buns are golden brown from both sides. Finally Serve toasted buns with bhaji, garnish with onion and butter.