I suggest you switch to salmon. Tasty, tasty fat and pretty foolproof to cook. Overcooked tuna and chicken breast taste like sawdust and really is not worth eating unless you want to use it as a tool to completely kill your appetite (I've found myself not wanting to eat anymore after having a forkful of overcooked tuna). I just pop a chunk of miso in a pot with some water and a filet of salmon and let it simmer; whether or not I've forgotten to check back on it after it's done cooking for a few minutes or 10 (oops), it's always still quite good despite my worst.
F 28/5'4/100 lbs
"I'm not a psychopath, I'm a high-functioning sociopath; do your research."