Heat butter in a pan, add onions and sauté till translucent.
Add capsicums, tomatoes, mushrooms, salt and sugar and sauté for three to four minutes.
Spread the pizza sauce on each bread slice and place the vegetable mixture over it.
Top up with grated cheese and place the slices on a hot tawa and cook till the cheese melts.
Cut into diagonals and serve hot with tomato ketchup.