Finding high fiber, nutritious, low calorie, very tasty filling foods were a challenge for me also. At first I just tried eating less of whatever I wanted but that quit working after losing 50 lbs. Then I had to change foods.
On my list so far with my favorites first... Okra. Squash, summer. Squash, winter. Mushroom. These can be cooked by themselves or with the others here, or with other vegetables.
I quite often make a large amount of a mix of squash, okra, mushroom cooked with tomato. Fresh, canned or both, or a sauce. Or they can be cooked into a pasta sauce and used on a bed of pasta or brown rice. Or brown rice mixed into it. Many many many ways to cook these very filling low calorie nutritious items and make them extremely tasty by using onion, green onion, celery, for added flavor, and seasonings such as coriander, different chilies, oregano, cumin, garlic etc.
They go great with a meat or meat of several types go well in them, such as chicken, pork and beef. I usually just eat them veggie. A cup of the above mix without the rice or meat is about 30 calories per cup.
Cucumber. Usually just a cucumber sliced and sprinkled with a chili-lime-salt type condiment made for putting on fruit, such as Valintino, Tejin, Trechas. Sometimes I add a cubed tomato or/and other mushroom/squash/orka with it. One cucumber will often keep me satisfied for 3 hours or more and is only 20 calories ! You could use a low calorie dressing instead, but my favorite is the chili condiments.
Saurkraut (home made, fermented, uncooked) by itself or with something, such as beans or rice. One cup 20 calories. And home made is very different than store-bought stuff. Very cheap and easy to make.
Seasonings, and first on that list is tomato, green tomato, green chilies, (jalapeno, serrano. Dried chilies.. Chili de arbol, japanese chilies, korean chili (used to make kimchi) which is used as a condiment. And cumin, cilandro, coriander, oregano, marjoram are my favorites along with the chilies. But different tastes can be made by using different spices such as curry powder, which will lend an Asian or Indian flavor to the foods.
Brown rice. Goes with so many things, is great by itself or mixes into many dishes superbly. It is 220 calores per cup of cooked though.
Beans. My favorite is pinto. But all dry beans cooked are about 220 calories per cup. I eat a lot of these, almost every day and sometimes more than once per day. Eaten with plenty of chili spices for me.
Eggs. Large eggs are only 74 calories (compare this to 100 calories for a slice of bread or tortilla. Or a bagel for 240 calories not including any spread you put on it! Or 120 calories for buttered toast. A one cup bowl of brown rice or beans with two large eggs would be a filling 290 calories.
These are my mainstays and work well for me. So many blends/mixtures for cooking them to make a nice variety of high fiber nutritious filling low calorie meals.
And you could also get into chinese cooking using the bok choy, bean sprouts etc... Many low calorie nutritious things out there for you.
Good luck with yours
B F R