Do you have a microwave at work? I just use old chinese takeaway cartons with rice and chicken - microwave for 2 mins and you're done. Although from your cold chicken - guess you dont?
Most bread has a lot of sugar in it. I think one sandwich a day should be ok. Try and get granary or wholemeal. Tesco do a good range. Some is low GI and other medium. Try the linseed bread which is low or oatmeal batch which is meduim. No more than 2 slices per day though IMO. I like pittas - not sure what really goes into them though so I can't really adivse on that. Wholemeal as a rule of thumb should be fine. Maybe try wholemeal tortillas as well. Nice and easy to role up with a bed of shredded spinach, chicken and some red peppers.
As for your chicken - try some tikka seasoning from tesco or even just cajun, fajita, chargrilled. Dry seasonings are usually a good way forward. Hey - you could even get Nando's piri piri seasoning which I hear isnt too bad. Nice and hot as well
. I sometimes use a bit of sweet chili sauce but that does have quite a lot of sugar in it :( .