In a large pot of salted boiling water, cook pasta according to package instructions. Drain.
Meanwhile, make dressing: In a large bowl, whisk together oil, vinegar, horseradish, Worcestershire, hot sauce, and celery seeds. Season with salt and pepper.
In the bowl you made the dressing, combine pasta, bacon, celery, tomatoes, green bell pepper, red bell pepper, onion, mozzarella, and olives. Toss with the dressing to completely coat
If you prefer, set aside the bacon and use it as a topping for those who don’t eat meat
On the onions: You can get rid of the strong taste by soaking sliced onions in ice water for 20 to 30 minutes or by sprinkling them with an acid such as vinegar. Onions soaked in ice water will get very crisp while those sprinkled with vinegar will soften a bit, but they will lose the strong taste and become sweeter.