Here is more on Mumbai sandwichwalas if you like a further read and if that's not enough make yourself this sandwich already.
Mumbai street inspired chutney sandwich
White bread w/o sides 4 slices
Butter a dab
For tempered potatoes- Boil potatoes in an open vessel and not a pressure cooker (pressure cooker makes the potatoes too soft) , peel and mash the potatoes and leave aside. Heat oil in a pan , when hot tip in a few mustard seeds once they splutter add in curry leaves and a slit green chilli , a pinch of turmeric powder, mashed potatoes and some chopped coriander leaves. Stir for a while and turn off the stove.
Assembly-
Cut the sides of two bread slices
Smear a little butter and coriander mint chutney on one of the bread slices
Spread a teaspoon of tempered mashed potato covering all the surface
Place a few slices of beetroot, cucumber,tomatoe and onions in the same order
Season with salt & pepper use a cheese slice if you like
Now close the sandwich the other slice of bread , brush a little butter on the bread and place it in a gas toaster or griller
Grill till golden brown on both the side
Serve with tomatoe ketchup or more coriander mint chutney
Update: I found a more authentic recipe Here
Variation - Boiled eggs can be replaced in place of all the veggies, it make for a superb sandwich too.

