I have had/ and do it 3 different ways
1) mash it up and spread
2) mash but leaves chunky and spread
3) slice and stack
Personally, I like the chunky version, but in general, all work.
Many years ago, I worked with a guy from El Salvador. He brought in lunch one day which basically was a baguette, a few avocados and a hard boiled egg.
He mashed the avocado with salt, placed it on the bread and then crumbled the hard boiled egg on it to make a sandwich.
Im not a big egg fan, but I can definitely see how the worked. So simple but so good.
to this day I often have avocado sandwiches on kaiser rolls ( I sprinkle salt and finely chopped onion). I prefer it more that the avocado toast ( cause I love rolls) but the toast is healthier since Im using one of those grain/ low carb breads.