As a vegetarian, sandwich options are a bit limited for me. They are usually just veggies and cheese and maybe some hummus, and that can get boring. A common addition is red onions, which are tasty and add a nice zing to the meal. However, for the rest of the day I feel like I have terrible breath, and also my hands smell like onions. I chew gum, and brush my teeth and drink a ton of water and wash my hands but it takes forever to go away. For that reason I really dislike eating raw red onions.
UPDATE: You can SOAK red onions in ice water for 10-15 minutes before using and that removes a lot of the bite and harshness from them. I'm cooking this recipe tonight and I'm using that trick. Hope it works or the rest of the night will be horrible.