rinse the tomato well. cut out top and bottom. slice.

cut off top and bottom of the onion. slice ( I rinse my onion before slicing )

heat up a frying pan with oil or butter. you can also use a griddle.

butter one side of each bread piece

place the butter side down on the pan or griddle

add a slice or more on top of this.

add some sliced onion on top of the tomato

carefully spoon on a bit of balsamic vinaigrette over top of the tomato and onion. you can spread it on the bread first but I found it didn't work as good

cook for a few minutes. dont burn the bread. use a spatula and move it around a bit

add the other slice of bread and top that with the cheese slice

put them together after the cheese starts to get warm. melt cheese through

flip if needed

serve hot with any side. enjoy

note : I liked this but I think I should have fried the onions just a bit before putting them on. I would say for maybe 2 to 5 minutes just to get them a little softer.