Since you are going to request an IEP meeting, and you are going to get a doctor’s note, I would consult with your son’s doctor about including in the letter a recommended timeframe for him to consume enough of his lunch. Just like your son would get more time on a test, ask for more time to eat lunch. Most likely, the school won’t like it and won’t be able to conceive of ways to execute it effectively or fairly, so come up with some options to help them find a way. For example, he could have a pass to take 5 minute break in the middle of class to eat/drink as needed (it could be limited to 2 times per day, for example), have 10 extra minutes to finish his lunch in class during the period after lunchtime, etc. For the actual amount of time, talk to your son and see how much time he actually needs with the goal being as little as possible because you do not want him to miss class or be late. Then, try to have the school work with him on making it possible without putting him at a disadvantage academically (e.g., eat in the nurse’s office or an administrative office until he finishes before going to class, because this would take too much time and being easily distracted he would likely miss too much time eating and/or traveling to his next class).