Boil the potatoes, peel and mash them.
Heat a pan and add oil. Let it become hot.
Add mustard seeds and let them crackle.
Add salt, ginger garlic paste, turmeric powder, coriander leaves, and fry for 10 to 20 seconds.
Add mashed potatoes and mix well. Fry on high flame while mixing for 1 to 2 minutes.
Add black pepper powder and mix well.
Prepare green chutney in a mixer jar by adding coriander leaves, green chillies, garlic cloves, salt, lemon juice, and make a smooth paste.
Apply butter on all the bread slices at room temperature.
Heat a pan and roast the bread slices lightly on one side.
Assemble the sandwich by spreading green chutney, potato masala, vegetables, cheese slice, and tomato ketchup.
Heat the pan again and add butter. Place the sandwich in the pan and roast for 2-3 minutes on low to medium flame.
Turn the sandwich over and roast for another 2-3 minutes. Remove from heat and serve hot.