I LOVE cottage cheese. It's a good source of protein, mine has like 11 g prot/ <1 g fat/ 3 g carbs per 100 g. So thats quite good.
I eat a lot of yoghurt too, but that has less protein. The only thing that worries me a bit is that its dairy, but i heard its more healthier than milk.
Usually i add sugar in it.
Fruit mixed in it is really good too, but i still add a drop of sugar then.
Pieces of lemon/banana is good, but the best thing imo is little pieces of apple.
Chop one or two apples in lil pieces, add some to your cup of cot cheese, and the rest in the fridge, its stays good for quite some time, longer then other fruits (cause its harder) and the next time you can use it.
Never tried tuna. You just add it straight from the can?
Maybe next time i'll try adding some olive oil in it, see how that mixes, i wanna raise my (healthy) fat intake.