Like many people on Avvo who have narrowly avoided eating something they didn't intend to when something was in their food that wasn't supposed to be there, you consider yourself lucky and you move on. You can report this restaurant to the food inspection agency in your locale if you want to. Since you noticed the metal piece, didn't eat it or suffer any harm, got your money back and an apology and a promise or payment for medical damages, you've already gotten what you were entitled to.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
There may not be much you can do. In order to have a valid personal injury case, you must actually have damages, for example the metal cut your mouth. Here, you have said "Luckily, I hadn't bite any part of the metal piece." It does not sound like you were injured.
If you were, consult an attorney.
It is excellent that you were not hurt. You will need to prove damages to be successful in a lawsuit. Disgust about a thin piece of metal will not be enough to make a lawsuit worthwhile.
Take your complaint about the product back to the store and perhaps you will get those coupons and another apology.
Good luck to you.
NOTE: This answer is made available by the out-of-state lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding.
I cannot suggest that you pursue any legal claim. Since you feel fine and are not sick at all, this falls into the "no harm, no foul" category. The restaurant's courtesy to you after you reported the problem is commendable. Good luck to you!
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