I once brought this veggie sub to a family picnic as an option for a few adults I knew wouldn't necessarily want to eat a stack of cured Italian pork for lunch. The adults were out of luck, though, because almost all the kids opted for the veg version over the meat. Below is what you will need for one twelve-inch sub to feed five people. Double or triple as needed depending on the size of your party. You can use the classic Italian red wine vinegar and oregano dressing for this since you probably already have that on hand - but also keep in mind that a basic vinaigrette works well, too.
Slice the baguette in half lengthwise and on the bottom half, start by layering the avocado then the cheese, slightly overlapping as you go. Lay down the cucumbers in two adjacent rows, overlapping slightly, on top of the cheese. Distribute the tomato halves, overlapping as well, then the lettuce and onion.
When ready to serve, whisk together the vinegar, olive oil, and oregano until emulsified, then drizzle on the top baguette half. Spread the mayo on top of the vinaigrette.
Close the sandwich with the top baguette half, then stick in 5 toothpicks, one every 2 to 2 1/2 inches along the top. Place on a cutting board and slice into 5 separate sandwiches.