How badly recessed is that jaw? I've seen people with iguanas with recessed jaws and many of them are quite bad to the point where owners have to rub water on the jaw daily to keep it moist.
Outside of that info.. If he is eating enough to keep his weight up.. Let him keep on doing this. Kill spinach and spring mixes, add endive and escarole. The idea with greens is give a mix of them.. They all contain a form of natural toxin, so you want to alternate them. Spinach is known to be quite high in these toxins, and spring mix generally has a lot of lettuces.. Which serve no dietary benefit. Fruits are good for water content but you do not need to feed them too often. You want approx 60ish percent in greens, then mostly veggies.. Bell pepper is more of a color stimulant FYI.. You can cut that from the diet.
One of the big thing with reptiles is stress.. Stress from human interactions and their surroundings. You might want to give the old guy some privacy for a while.. And if he's in a room with other reptiles that may be driving him bonkers too..