Can you sue a restuarant? ?

So we went to a restaurant that the time before we went we found out that they cook their sweet potatoes in LARD, and not to mention we CANT eat pork (religious) and so we said ok we won't order it! So we decided to come back and just a wondered question we asked the manager to see if it was true and he said yes and he said that all of our food is cooked with some type of pig, pork , lard whatever it is! And the whole table is in shock we all drop our food and start to wonder if we can even continue our food we asked if the prime rib is cooked in lard and he said no that is the only thing other than fries salads the apple sauce is not cooked in lard so there went our potatoes ! So just a curious question could we sue for the failure of not warning or saying anything? And when we asked the manager he was like we can't telll you its a secret !! I was like its not a secret when it is a risk and if its against someones religion or how about if their a vegetarian ! Please help thank you!