Finely chop carrots, celery, onion or scallions. If you have a food processor or small mixer, you can put it all in that. Chop cheese into small pieces.
Then drain tuna well and add everything to pasta. Then add salt, pepper, some onion powder, mayo, and mix it all around. I usually eyeball the mayo, but you want to put a nice amount in since the tuna absorbs it.
Then put it back in the fridge for a few hours before serving. I usually add more mayo right before I serve it because it might be a little dry.