Raw, organic nuts and dried fruit are great filler-uppers. Almonds and walnuts are very nutritious. We always keep those around (along with cashews and pistachios) to snack on. Another option for your meals are sweet potatoes and winter squash.
I've recently realized that marketing execs have us all thinking that veganism is a huge stretch and something totally "other" than what "normal" people eat. Allow me to address this with a picture: http://sneakyvegan.blogspot.com/p/faqs.html
If your goal is to be more health-conscious, try searching for vegan/vegetarian athletes who share their menu plans. I spent years as a personal trainer and had a monstrously huge boyfriend and although we both loved to eat "real food", butter, cheese, milk and animal products didn't appear on our menu plans very often at all. Make it easier on yourself by going slowly and maybe having 1-2 vegan meals/week from recipes that use real food. You can experiment with "substitutes" later but I think it's easier to make a switch if you change as little as possible in the beginning. Take time to build a collection of vegan recipes that you really like so you won't feel so deprived. Eventually you will find enough food to keep you satisfied and can slowly increase the number of vegan meals you eat.
If you feel like you're starving a couple of hours after eating that's good! It means your metabolism is working and you're using up all the calories you're taking in. Most athletes eat 6 times a day - 3 full meals and 3 snacks. This means you're eating something every 3 hours. Keep healthy snacks at your office like fruit, nuts, baby carrots. Invest in blender and keep it in the office kitchen - when everyone else goes for a smoke break, make yourself a smoothie.
i'm a vegetarian and try to eat vegan around 75-80% of the time. check out my blog, blakebakes.blogspot.com for some easy, satisfying recipes. and to reiterate what most others have said, protein! especially beans, in all forms. cheap, easy, tasty, and filling. also, try limiting the pasta and bagels (unless whole wheat) because those are refined carbs that just make you hungry faster.
I was really hungry in the beginning too. I was so used to severe food restriction when I was eating "the old way" that when I removed so many unhealthy foods, I wasn't eating enough and was really hunger. I started eating more often and enjoying grains, beans and legumes like I never had before. I thought of these foods as too many calories before. Well they are when you have them with meat, cheese, sauces, etc. But on their own and whole they are great for fiber and sustained energy.
Wow! I sit here stuffed contiplating this idea of being starving. Of course stuffed is different now than it used to be. I am vegan but also gluten free and sulfite free (which means no processed foods) You don't have to be hungry to be vegan!
For breakfast this morning I had left-over brown rice topped with nuts and banana, for lunch I just had 1/2 a baked sweet potato and left-over bean & veggie soup. Make sure you have left-overs you can grab when you are in a hurry! That is my tip.
By the way I am not hungry and am losing weight and feel great!
Another thing to remember... If you are newly flirting/vegan, you may be used to feeling "full" all the time, then when you don't feel "full", you feel hungry. It may take a while of plant-based eating to get used to feeling lighter. After a while, you won't feel as hungry because your body will be used to the way you are eating. It tooke me a couple months to get over this, and sometimes all it took was to stop and think: am I hungry, or am I just not feeling full? And if I am really hungry, I eat something! Having a healthy snack around is a good idea.
All this assuming you are eating a nutritionally balanced diet. Some of that just takes practice; after a while, you won't have to think about whether you are eating enough of each food group, you just will out of habit.
As has been said adding beans/legumes to your diet are easy and filling. Rich in protein and fiber so will satisfy your appetite.
Nuts and seeds are also good, there are also many raw/vegan bars you can buy which are healthy and very filling. Dont forget fruit also, eating a few bits of fruit inbetween meals can be really helpful.