Inspired by this Ask Metafilter thread and the sandwich combining avocado with honey mustard that was described therein, tonight I made some avocado sandwiches of my own. We ate them standing up in the kitchen, making adjustments as we went: open-faced, because when you use as much avocado as we wanted to, closed-face versions just slide around; an extra sprinkle of salt; slivered red onions to gild the lily.
Like salads, most sandwiches don't really call for recipes, just descriptions. To make these, take a baguette and split it lengthwise, parallel to the table. Cut the resulting halves into pieces of whatever size suits you. Next, generously butter the cut sides of the bread with nice, soft salted butter. Now apply a good helping of avocado, mashing it slightly into the bread. Because the base of your sandwich is all crust, it will stand up to the pressure with no trouble. Sprinkle a little salt over the avocado and then add a generous (a theme with this sandwich) coating of honey mustard, which you have made by mixing equalish quanities of dijon mustard and honey.
This is very good as it is. But after we'd tried it, Snark said, "Is there any one ingredient that would make this even better?" That is how we wound up adding red onions, and also how I wound up eating quite a bit more than I had planned. In fact, if we hadn't used up all of our ripe avocado I would be eating even more right this minute.