Boil the pasta. Bring a pot of salted water to a rolling boil and add the pasta. Cook according to package instructions until al dente. Drain and rinse with cool water.
Soak the onions. This is an optional step, but I find that it takes some of the raw onion heat away. Soak the thinly sliced red onions in very cold water for 10 minutes, then drain.
Mix the dressing. Whisk together the mayonnaise, dijon, red wine vinegar, oregano, sugar, salt, pepper, and olive oil together until smooth.
Mix the pasta salad. Mix the onion, salami, red peppers, pepperoncini, pickled peppers, cherry tomatoes, and mozzarella into the dressing. Season to taste with salt and pepper. Add the pasta and fresh basil and toss well to combine. Cover and refrigerate until ready to serve.