Bring a large pot of salted water to a boil and cook the rotini pasta according to package directions until al dente. Drain the pasta thoroughly, then rinse it under cold running water until completely cooled. This stops the cooking process and prevents the pasta from becoming mushy when mixed with the creamy dressing. Set the cooled pasta aside.

In a large mixing bowl, combine the mayonnaise, mustard, apple cider vinegar, sugar, salt, onion powder, celery seeds, black pepper, and fresh lemon juice. Whisk everything together until the dressing is smooth and well-blended, making sure the sugar and salt are fully dissolved. I like to taste the dressing at this point and adjust the seasoning—if you prefer it tangier, add a splash more vinegar, or if you want it sweeter, add a bit more sugar. The dressing should taste slightly bold since it will mellow out when mixed with the pasta and vegetables.

Add the cooled pasta from Step 1 and the coleslaw mix to the dressing bowl. Using a large spoon or rubber spatula, gently toss everything together until the pasta and vegetables are evenly coated with the dressing. Make sure to fold from the bottom up to avoid breaking the pasta and to ensure even distribution. I recommend letting the salad sit for 15-20 minutes before serving so the flavors can meld together and the coleslaw softens slightly—this also gives the pasta time to absorb some of the dressing for better flavor.