Journal, journal, journal!
Cell phones have made this remarkably easy! Take a picture of everything you eat! Notice how much food is there. Spill the salt shaker and write the number of your hunger level on the table in salt and take a picture of your full plate next to it! Anything! People, please!
Seriously! Figure out how you can journal -- paper, app, photo -- there's no wrong way. The idea is to get some concrete evidence you can refer back to so you can start figuring out when you over-eat (perhaps it's all the time or maybe it's only when you've a stressful late afternoon meeting). Figure out when you leave the table feeling light and refreshed -- can you remember the last time that happened? --You'd be able to if you journaled!
You're looking for patterns. What drives you to eat more than the amount that makes you feel good?
What happens right before you sit down and eat the right amount of food that leaves you satisfied but not stuffed?
Don't know?? JOURNAL! Easy. Simple. Inexpensive. What's the problem here??? Are you telling me your health (and your sanity) isn't worth the tiny bit of time and attention journaling requires? Well....then there might just be the problem.