Cook the pasta in salted water according to package instructions for 8–10 minutes. Drain and rinse under cold water.

Prepare the vegetables: slice the red onion, dice the cucumber, halve the cherry tomatoes, and chop the arugula.

In a large mixing bowl, whisk together mayonnaise and sour cream; season with salt and black pepper.

Combine the cooled rotini pasta with the dressing, fold in the vegetables and arugula until evenly coated.

Chill the salad for at least 30 minutes before serving to allow the flavors to meld.

Stir before serving and add extra dressing if needed.