I don't think protein bars are the way to go either, so many of them are really sweet and they aren't filling though they're often very calorific.
We have porridge made with skimmed milk some days, eggs in some form for breakfast every day and snack on roasted (unsalted) nuts of various kinds. Our other meals are pretty normal protein and two veg types.
We also like lentils prepared in various ways, some spicy, some just savoury, which can be eaten as an addition to a main meal. You can get them ready to eat in store cupboard sachets or cook yourself a batch every few days, flavouring to suit the meal you're having.
I also agree with other posters that tinned fish is a really good way to add protein. Sardines in various forms are lovely for a snacky lunch and tuna in spring water is good in sauce with pasta or with a jacket potato.
We also like risotto and find that smoked mackerel is good in this, added near the end so it doesn't disintegrate to much.