this sounds exactly like me when I ate too fast, or a texture I wasn't ready for yet. I would get a terrible chest pain that took a moment then passed. never nauseous or regurgitated anything, it just HURT right in the centre of my chest.
here are my suggestions to you:
1. buy yourself a smaller set of silverware and a small plate to help you adjust to eating small bites. I've heard the size of your pinky finger tip. sometimes you just have to trick your brain with an optical illusion to help you relearn what size bites are really right for your stomach.
2. use a timer to time your chewing. Baritastic is an app that has a "chew chew chew" timer built right into it. use the timer and make sure you are chewing that entire time, even if the sensation starts to be kinda gross. you will eventually be able to chew a BIT more normally, but for now you really need to destroy everything that goes into your mouth.
3. PUT YOUR FORK DOWN between bites. do not chew, swallow, put more in the your mouth, because you'll think you're taking your time but you may be eating wayyyyy faster than you perceive yourself to be. (this is especially true of moms or teachers or nurses or anyone who has had a lifetime of needing to eat fast and get onto the next thing ASAP... those habits die hard lol!) take a bite, put your fork down, chew, swallow, sit and breathe... then take another bite.
If you are chewing slowly and small bites and still getting that sensation, take a break from the food that causes that sensation and try something else. the first time i got it was from some mashed potatoes. I stopped eating them, had something else, and didn't try them again for another couple weeks (since they're not that great of a food for you anyway). for something like eggs that fits well into your post-op diet, try them the next day or two days later maybe.
you can also try cooking the eggs a different way. some people can't do scrambled eggs but can do poached, etc.
tuna, if you haven't yet, try mixing it with some kind of sauce, whether that be light mayo or yogurt or vinaigrette or whatever else you like. I had mine with light miracle whip.