First, chop the cucumber, tomatoes and onions in thin round slices. Peel and slice the beet and potatoes thinly.
Take 1 cup tightly packed coriander leaves, ½ teaspoon cumin powder, 1 teaspoon chopped green chillies or serrano pepper (1 to 2 green chilies)and 1 to 2 chopped garlic cloves (small to medium-sized) in a chutney grinder jar or food processor.
Add and ½ to ¾ teaspoon lemon juice, ¼ teaspoon black salt and white salt or rock salt as required. Grind the chutney ingredients till smooth. If you cannot grind, then add 1 or 2 tablespoons of water.
Transfer to a bowl.
Using the bread slice of your choice (whole wheat, white or brown), spread a relatively liberal and even layer of butter on the inside slices of your bread. Spread a thin layer of chutney over the butter.
On one slice, layer rounds of potato. Sprinkle with a pinch or two of chaat masala and roasted cumin powder.
Layer with tomato, onion, cucumber slices and beet slices (if using them). Add another pinch or two of chaat masala and roasted cumin powder, and finish with some black salt.
Top with your other slice of bread, chutney side in. Spread a thin layer of butter on the outside layer of the top bread slice. Preheat your grill. When warm, flip the sandwich so the butter side goes down. Butter the outside of the now top piece of bread.
Close the grill lid and grill for 2 to 3 minutes, until golden and crispy.. Serve grilled sandwich hot or warm with a side of green chutney or tomato ketchup.