Mix mayonnaise, salt, pepper, onion, carrot, capsicum and red chilli flakes in a bowl.
Apply butter over bread slices.
Keep some filling over one bread slice and cover with another slice.
Slather little butter on both sides the sandwich and toast the sandwich.
Cut into triangle and serve hot.
For the vegetables, I have used onion, carrot and capsicum, but you experiment and add vegetables of your choice such as corn, mushroom, green peas, cucumber, potato, shredded cabbage etc. You can even use boiled eggs, scrambled eggs, tuna or chicken instead or along with vegetables, to add some extra protein your daily diet.Slather the bread with some green chutney before adding the filling for a tangy twist.To make it vegan, use eggless mayonnaise and oil in place of butter.You can even use flavoured mayonnaise in place of plain one.Make it with brown bread in place of white bread for healthy version.