First boil the potato and peas.
Take the potato in a pressure cooker. Add enough water. So potato is submerged in water.

Cover the pressure cooker, put the weight on. Turn the heat on medium heat. Cook for 2-3 whistles or till potatoes are soft.
Let the pressure go down by itself, open the lid.

Remove the potato. Let it cool to touch, peel it and roughly mash it.
For cooking green peas, I have taken them in a microwave-safe bowl. Add a tablespoon of water. Partially cover it and cook for 4-5 minutes.

Alternately you can boil in pressure cooker or steam them.

Meanwhile potatoes and peas are cooking, slice the onion, tomato and cucumber for the sandwich and keep it aside.

Heat the oil in a pan on medium heat.
Once hot add mustard seeds. Let them pop.

Then add cumin seeds. Let the sizzle.
Then add ginger paste and green chilies. Saute for a minute.

Then add chopped onions. Cook till onions are soft and light brown in colour.
Add turmeric powder, red chilli powder and salt. Mix well and cook for a minute.
Then add mashed potato and peas. Mix well. So all the spices are coated and everything is incorporated well. Cook for 2 minutes.

Then turn off the stove.Sprinkle chopped coriander leaves.Lastly squeeze lemon juice. Mix well and keep it aside

I make One sandwiches at a time because my sandwich toaster can accommodate one only.

Spread the butter on four bread slices.
Then also spread the chutney on all the slices. Then on bread slices, spread the even layer of potato masala. 2-3 tablespoons of masala is enough for one sandwich.

The arrange the cucumber, tomato and onion slices on top.

Close the sandwich with another bread slice (chutney side down).

Now toast the sandwiches in the toaster.