People may be eating what they choose to eat with just as much moral conviction as your vegetarianism. That is not for you to decide.
You have no right to deceive others about what they are putting into their body, let alone in hopes of "convincing" or converting them.
You have no right to physically force your own morality upon others without their informed consent.
Think about what you have just argued for here.
On top of that, it's very likely that every ingredient in the "turkey loaf" was something that would not be out of place in an actual turkey loaf. In other words, no ingredients being secretly added, just one being removed.
So again here there is a difference adding a problem ingredient, and there being an ingredient you don't put in. For the former you need to ask about dietary restrictions and respect that. Which they did. For the latter, I don't think you're in much risk of violating anyone's moral system.
If it's unrelated to GMOs, I'm genuinely interested in what your objection might be.