Looking for advice on cheap but filling food items that are not carb based.

Hello! Life has hit us in the face repeatedly this last year and I’m desperately looking for ways to cut back. I’ve cut out almost all subscriptions and have stopped nonsense shopping, but I feel like we spend too much on food. The issue I have is that my SO has a huge appetite and dietary restrictions. He can’t have gluten and is not supposed to eat carb heavy foods, like potatoes, rice and beans. This is due to his pre-diabetes diagnosis and cutting out these foods has helped get his blood levels where they are supposed to be. He is trying really hard to maintain this lifestyle. He has thyroid issues on top of this, we don’t want to add more medical problems or bills to our tab. What are filling and cheap foods that we can supplement our meals with that fall into his restrictions? He actually loves healthy foods but can eat a whole head of broccoli in one sitting with a protein and still be hungry. I’m at a loss of what to shop for or make.

Edit to clarify: the gluten restriction is separate from the carb restriction his doctor gave him, one is thyroid based and one is diabetes based. He does allow himself to eat carbs on a limited basis, but it cannot be used to bulk up all our meals