Cook the pasta as per the instructions on the package. After cooking, drain and rinse with cold water until the pasta is cooled.
Prepare the Italian dressing in a large mixing bowl. Whisk together the olive oil, vinegar, lemon juice, Italian seasoning, sugar, garlic powder, and red pepper flakes.
Add the cooled pasta to the dressing and mix well.
Add in the tomatoes, mozzarella, olives, chicken, pepperoncinis, and onion, tossing them to combine well.
Cover the bowl with plastic wrap and refrigerate for an hour before serving.