Chamchi deopbap is the dish Korean students live on. A tin of tuna, a spoon of gochujang, whatever vegetables are in the fridge and a fried egg on top, all built over hot rice in about the time it takes the kettle to boil.
Do not skip warming the tuna through with the onion and sauce. Two minutes in the pan turns it from something out of a tin into something that tastes cooked, and the raw cucumber and carrot on the side keep it fresh rather than heavy.