Freezing sandwiches for toasting at work
Freezing them will cause the cells to break down slightly, leading to a mushier vegetable. However, since you're planning on heating them anyway, I wouldn't worry about that. Heating will also make the vegetables softer and mushier, so I doubt that the initial freezing will significantly change the quality of the final hot sandwich. I would personally attempt to cook them straight from frozen if you have a freezer at work. The vegetables can release liquid over a slow defrost in the fridge which may affect the structural integrity of the bread.