Cook pasta according to package directions. Drain and rinse with cold water.
Saute chicken breasts in olive oil. Sprinkle with garlic powder and brown on both sides. Cover and simmer over medium heat until cooked through, approximately 8 minutes. Cool and dice.
Combine pasta shells, chicken, red onion, celery, and radishes in a bowl. Toss with ranch dressing. Season with salt and pepper. Chill.
