Since I've always been fairly active, I've never had huge variations in weight (though I did like to gain/lose 10 lbs repeatedly, so vexing).
What worked for me was just gradually increasing my veg and bean intake with everything I eat. I eat whatever I want, I just can't eat too much of it because of all the veg and beans filling me up. Basically: all naturally high fiber foods are naturally low in calories, and fill you up very effectively (for me, far more satiating than protein, whilst also being lower calorie).
Our gut microbiome needs to be changed slowly so that it has the time to propagate the necessary microbes to digest whatever we're eating a lot of. I started by adding just a handful of spinach to my curry / spaghetti etc. Then after a few weeks I added a spoonful of lentils. Etc etc until I'm easily consuming huge amounts of greens and beans/legumes when I eat, and too full to eat dessert even if I wanted to.
Oh and if I'm stressed I try to eat fruit and nuts more frequently especially in the morning when I'm more motivated.
So this might be a stressy day:
-usual breakfast of porridge (microwave oats for 1m20, add frozen blueberries and cinnamon, then microwave another minute. Add chia seeds and ground flax)
-within 2hrs later: have an apple / piece of fruit
-very filling early lunch (either cook something, or have leftovers, or a sandwich. Sandwich will either be PBJ or a hummus sandwich spread quite thickly with hummus, or a very easy burrito I've been enjoying lately, can provide details if you like). Frozen broccoli always on the side too / mixed in, only 3-4 florets is needed for a serving. Start with one or two and build.
-asap have more fruit / nuts when I can, and try not to listen to the stupid 'nah I'm actually FULL' voice that'll want me to eat more later if I don't preemptively silence it. (Often we're 'full' for healthy food but not for junk...most people wouldn't eat a second apple, but don't hesitate for a second slice of pizza)
-dinner: I eat something quite light, if I had eg pasta for lunch then I might have some grapes, it's probably all I have room for tbh. Carrots and hummus (maybe some grape tomatoes too) if I need extra.
Microwaving greens wilts em really fast, you can pile a plate very high with eg kale, and after just a minute it's down to nothing and will mix easily into whatever.
Basically for me, processed food is too addictive when I'm stressed so I stick to minimally processed stuff (eg pre-made hummus, low-sodium tins of beans etc).
I stopped cooking with oil too as oil is just excess calories, you can water fry (with plain water or broth). Fat, salt, and sugar encourage my appetite too much, but fortunately plants have fiber which help stabilize the blood sugar, which helps lead to much fewer cravings.
Feel free to pm if you have any questions. I'm kinda confused how much I still go through all my healthy habits, but I guess it's worth it because physically at least it does help. Whatever else I do wrong, no one could fault my diet / exercise / sleep routine........
Good luck x