I sometimes do a big bowl of pasta salad. there's usually enough for a couple of days. I make it the night before and put it in the fridge ready for the morning.
I boil up pasta, any shape will do.
In a bowl I mix tuna, sweetcorn, peppers, dill, chives, red onion, fresh peas and whatever I can find. And then mix with mayo and seasoning. Once pasta is done I run it under the cold tap and then drain the water and mix with the rest.
V. yummy
I also bring Ryvita to work and have them with different sandwich toppers.
I haven't eaten sandwiches for years as like you say they get sooooo boring. Look forward to seeing other suggestions on here.