Losing weight- How do you get full?

Okay, so I’ve just started my weight loss “diet” yesterday, and today i had a big bowl of tuna salad for lunch and I’m just not full.. i ate an apple after and I can’t get full. I just want to eat more. I didn’t eat that much before either, I just feel like the stuff i ate was more filling (bread, pasta, ...) What should i eat to not still be hungry, but still be loosing weight ?