Heat 2 tbsps olive oil in a non-stick pan and 1 tbsp oil in another non-stick pan.
Add chopped onions to the first pan and saute till lightly coloured.
Add onion slices to the other pan and saute. Sprinkle a little salt on the onion slices.
Add soya granules to the first pan and saute. Add green chillies and ½ tsp red chilli powder and mix. Add salt and whole wheat flour and mix. Saute for 2-3 minutes.
When the onion slices caramelize, transfer them into a bowl.
Put soya mixture into a big bowl. Add mashed potato, brown breadcrumbs and mix well.
Heat 1 tbsp olive oil in another non-stick pan. Halve the brown bread buns and grill them in this pan.
Divide soya mixture into 4 equal portions and shape them into tikkis to suit the diameter of the buns.
Spread refined flour in a plate, add 1 tsp red chilli powder and salt and mix well.
Remove the buns from the pan and set aside.
Roll the soya tikkis in the spiced flour. Heat 1 tbsp olive oil in a non-stick pan, place the tikkis in the pan and cook, turning sides, till both sides are evenly golden and crisp.
Apply some tomato ketchup and mustard paste on the lower halves of the buns. Tear a few iceberg lettuce leaves and place over the lower halves. Sprinkle salt and crushed peppercorns and place the halves on a serving plate.