I came across Gina's tasty looking Greek Salad Sandwich recipe, which is full of vegetables:

I did substitute a few ingredients from her recipe- like the ciabatta bread (I used flat bread) and the red wine vinegar (I had balsamic vinegar and read that it's a fine substitute).
For this sandwich I added balsamic vinegar to my sliced red onion and sliced Kalamata olives. I let that sit while I prepared the rest of my sandwich. I layered all the vegetables- sliced tomato, sliced cucumber, lettuce- and added feta cheese to the flatbread. Finally, I added the red onion and Kalamata olives to my sandwich, and voila!

Done and delicious!
** I am attempting to make 52 sandwiches. Read more about how this project got started here. See all the sandwiches I've made so far here.**