Bring a large pot of lightly salted water to a boil; cook rotini at a boil until tender yet firm to the bite, about 8 minutes. Drain and let cool, 10 to 15 minutes.
Mix rotini pasta, tomatoes, cucumbers, olives, Italian dressing, Parmesan cheese, salt, and pepper together in a large bowl. Chill until flavors combine, about 1 hour.
Toss avocado with lemon juice in a bowl. Mix into the pasta salad before serving.
