Combine finely chopped onion, capsicum, carrots and cabbage in a mixing bowl.Add mayonnaise to the chopped
vegetables.Season with salt, black pepper and optionally some chaat masala or amchur (dry mango powder).Mix all the ingredients well to make the filling.

Spread some butter on one side of a bread. You can cut off the edges of the bread if you want.Spread out a large spoon of the filling evenly on the bread and close with a second piece of bread to make a sandwich.Lightly butter or oil the bread from outside and place on a grill, sandwich maker or pan.

Toast the bread till both sides are lightly brown and crispy.Mayonnaise sandwiches are ready. Serve them hot on their own or with tomato ketchup or green chutney.