I make (breadmaker) bread with 100g of gram flour and 500g of ordinary white flour. It comes out slightly yellower and dries out quicker (like 2 days), but is otherwise acceptable to my picky eaters. If you add an egg or two in place of some of the water that makes it last slightly longer before it dries and adds yet more protein. Don't add more than 1/6th gram flour though, or it doesn't rise...
I tried using gram flour in yorkshire puddings, but that was a floppy failure.
Making bread is my easiest way of adding protein - mine will now eat bread with bits in it, so sunflower seeds, pumpkin seeds, walnuts and things like that are really easy to add, as well as extra eggs.
I also make 'stealth nutrition pancakes' which are a mixture of ordinary flour, buckwheat flour (might work with gram flour instead), loads of eggs and a tin of white beans (butter, canellini, that kind of thing). The kids get an eggier version and the grown ups a less eggy one (make the batch in the liquidizer, pour off about 2/3 for the adults, then add extra eggs for the kids ones).
Flapjack? Mine have it with some combination of pumpkin, sunflower, poppy, sesame and flax seeds, poor little sods. Of those, pumpkin are probably the ones most likely to be rejected because they're a different colour from the surrounding yellow-ness. Ground flaxseeds are really easy to hide... (but don't use too much or it turns them out).
I may be a little obsessive about getting enough protein into my (veggie, picky) children...