Put the tuna chunks into a large enough bowl - you'll be mixing several ingredients later so make sure they'll all fit. I recommend not to drain the oil as I learned by experience that it tastes better when moist with oil but drain it if you think it's necessary. With a knife, slice through the middle of the salted egg then use a spoon to scoop out its contents into the bowl where you placed the tuna in a while ago. Be wary of shell fragments. You wouldn't want some crunchy calcium bits in your salad, right? If you used a dyed egg be prepared to have dye stains on your fingers. Don't worry, they can be removed with a few hand washes with some soap but let's continue with the dish first. Using the same spoon that you scooped the egg with, chop the egg into small pieces while gently mixing it with the tuna. Slowly add the onions, scallions and tomatoes and sprinkle some ground black pepper to taste while mixing. Gently mix them all together until they are distributed well within the tuna chunks. I prefer to have larger chunks of tuna and salted egg but you may continue mixing to turn them into tiny pieces if you wish. You're done! You may wash the dye off your hands now (assuming you used a dyed egg), get some rice and start om nom noming. The recipe should be enough for two to four people depending on how hungry they are. Enjoy!