Bring a pot of salted water to boil. Toss the tortellini and cook following the time on the package. Drain them, then cool down immediately under cold water until the pasta is completely cold. (See notes)
Meanwhile, chop the cherry tomatoes into small chunks and add them to a large bowl. Season with olive oil and salt.
Add the cooled tortellini to the bowl and add the red pesto sauce. Season to taste, then mix well with a spoon and cover the bowl with wrap. Add the mozzarelline on top
You can let it rest in the fridge for a few hours or serve it immediately. You can serve it with fresh basil leaves and a drizzle of chili oil or extra-virgin olive oil.
Notes
How to avoid overcooked sticky pasta: The secret to making the perfect pasta salad, is to drain the pasta al dente, then cool it down immediately under cold water until the pasta becomes completely cold. This way it will stop cooking and it will perfectly stay al dente for many many hours. Washing the pasta will also remove the starch so it will not be sticky.