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.
"How to Celebrate Everything: Recipes and Rituals for Birthdays, Holidays, Family Dinners and Every Day in Between" by Jenny Rosenstrach © Ballantine Books 2016. Provided courtesy of Jenny Rosenstrach. All rights reserved.