Whisk the mayonnaise, Parmesan, sour cream, lemon juice, Worcestershire, garlic, 1/2 teaspoon salt and a few grinds of pepper together in a large bowl.
Add the pasta to the boiling water and cook according to the package directions. Drain and rinse under cold water to cool. Add it to the large bowl and set aside.
Prepare a grill or grill pan for medium-high heat. Sprinkle the chicken breast with salt and pepper. Lightly oil the grill grates or grill pan. Grill the chicken, flipping once, until well-marked and the internal temperature registers 165 degrees F on an instant-read thermometer, about 7 minutes per side. Transfer to a cutting board and let rest for 5 minutes, then cut into 1/2-inch pieces.
Add the grilled chicken, romaine, celery and tomatoes to the bowl and toss to combine. Season with salt and pepper. The pasta salad is best if served right away.
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