Set a generous pot of water on the stove to start boiling.
Cut the tomato into bite-sized chunks; set aside.
Open the tin of tuna, drain it, and flake it with a fork. Set aside.
Cook the pasta according to package directions until just tender to the bite. Drain and return to pot.
Stir in the pesto and oil, then toss in the tomato and the tuna. Transfer to a bowl and set in fridge to chill. Bring to close to room temperature before serving.
Instead of using regular tomatoes cut up, you can use a few handfuls of cherry or grape tomatoes.Put in more pesto and oil, if you wish, or less.You can make this ahead of time, up to two days. Be prepared to refresh it with a glug of oil, and maybe more pesto, if the pasta has absorbed it all.You really want your pasta to have a nice "bite" in this salad, so don't let it go past "al dente."Optional: chopped up cucumber, sliced black olives.