For the Bhaji : heat oil in a pan, add grated ginger, let it turn brown, add capsicum and onion, saute for 2 mins. add tomatoes and let the tomatoes cook properly, now add pav bhaji masala, salt, saute for 1 mins. Add boiled potatoes and veggies and mash them using back of a spoon and mix well.

Add ketchup and let it cook for another 5 mins. Take it out in a container.

For White Sauce :

Heat pan add butter, add maida and cook maida in low flame for about 4-5 mins.

Add milk slowly and stir it continuously so that there is no lump formed. add salt, black pepper and mix well. if you find the consistency of the sauce to be thick then add vegetable stock till you get the desired consistency.

To Assemble.

Take a oven dish, grease it with butter, take buns and cut it into half, place buns on the greased tray, put bhaji on the buns., then put white sauce, grated cheese, then bread crumbs and decorate using capsicum and tomatoes. 

bake in a preheated oven for 15 min or till the cheese turns golden brown. Serve hot.