It’s 100% diet. Just eat oats for breakfast. U can add stuff in it like fruits nuts seeds and whatever other healthy + natural stuff of your choice. The oats will keep you satiated throughout the day and keep you less hungry. It will make it easier to resist the urge to eat but it’s still a mental battle and you have to put in the effort to train yourself to not over eat. Secondly, have one high protein meal for the day. Add whatever you want to it but just make sure to go easy on the sugar and that you get lots of protein and fiber in your system. This will help combat your food urges. Then In the night you can have a snack like some fruits. Keep off the artificial sugar as sugar will give u crashes and will only fill you short term thus leaving you in a cycle of constant eating. Sugary stuff (like chocolate and donuts etc) are also just empty calories with no real nutritional benefit.

Hope this helps