One tip I have that's pretty simple it breakfast:
Oatmeal such as rolled oats or steel cut, high in fiber and very filling.
Typically if I have rolled oats I mix in something like peanut butter and I'm good until lunch.
The steel cut oats I make more like a stew and throw in carrots, celery and garlic and make it a savory breakfast sometimes to thicken it up I'll also cook in 2 egg whites.
Both of those are low calorie and high in fiber.
Another trick I'll use if I'm finding myself super hungry at lunch is puree some sort of beans and make a bean patty out of them with some egg whites.
Once again high in fiber, low in calories and fills you up since it is relatively low calorie so you can eat more to fill the stomach.