Bring a large pot of salted water to a boil, then add rotini pasta. Cook according to package instructions until al dente, about 8-10 minutes. Drain and rinse under cold water.

Heat a grill pan over medium-high heat. Season chicken with salt, pepper, and olive oil. Grill for about 6-7 minutes on each side until internal temperature reaches 165°F. Let it rest.

Dice avocado, halve cherry tomatoes, and chop red onion. Soak onion in cold water for about 5 minutes. Gather chopped basil.

In a mixing bowl, combine cooked rotini, sliced chicken, diced avocado, cherry tomatoes, drained red onion, and basil. Toss gently to mix.

Drizzle salad with olive oil and vinegar, and sprinkle with salt, pepper, and Italian seasoning. Toss to combine.

Gently toss salad to mix dressing and ingredients; serve chilled or at room temperature.