here is the thing about apples: they aren't a very good snack choice. why you ask? because they're basically pure carbs. and snacks, just like meals, should have carbs and fiber and protein and fat. i mean, come on, has anyone every gotten full eating celery? no.
and when you eat pure carbs, be it an apple or plain sugar, you eat it, you use the energy and you get hungry again very quickly. the fiber in the apple is going to minimize the level of the sugar spike and stretch it out a little longer, but that's what is going to happen. so you need to find some fat and protein to go with that apple so that when the carbs get used up, there is protein waiting. a bit of cheese or some nut butter or nuts are great options to do this. otherwise, you're just piquing your appetite and setting yourself up to nibble at whatever is nearby.
as far as eating goes, you need to drill it into your head that it takes 20 minutes for the memo that you're full to go from your stomach to your head. and you need to find a way to wait out those 20 minutes after you finish eating before you go back for more. it can involve doing anything but sitting at the clock waiting for 20 minutes to pass. go for a walk, pick up a crafting hobby, clean, essentially distract yourself and you should not feel hungry when done.
another thing you might try is snacking all the time instead of having meals. and by snacking, i am talking eating balanced mini meals six or more times a day. it means you never really get hungry and you never really get full, you kinda stay more in the middle.
-google first. ask questions later.