Make the Ranch Dressing: Add all dressing ingredients to a mason jar, add cold water one tablespoon at a time, seal tightly and shake hard for 20 seconds. Taste, adjust salt, and refrigerate until needed.
Boil the Pasta: Cook the pasta in heavily salted boiling water to al dente, about 1 minute less than the package says. Drain immediately and rinse under cold running water until fully cool. Shake the colander well and let it drain thoroughly before using.
Crisp the Bacon: Cut the bacon into small pieces and place in a cold dry pan. Bring to medium heat and cook until deep golden and crunchy, about 6 to 8 minutes. Drain on a paper towel-lined plate and set aside.
Prep the Mix-Ins: Halve the cherry tomatoes, finely dice the red onion, and pull the rotisserie chicken into medium-sized pieces.
Assemble the Bowl: Add the completely cooled pasta, shredded chicken, tomatoes, and red onion to your largest mixing bowl. Toss gently until evenly combined.
Dress and Coat: Pour half the ranch dressing over the ingredients and toss well. Keep adding gradually until every piece is well coated but not drowning. Season with salt and black pepper and stir in the fresh parsley if using.
Add Bacon and Serve: Scatter the crispy bacon on top right before serving so it stays crunchy. If chilling first, keep the bacon separate and add at the last minute. Serve immediately or refrigerate for up to 1 hour before serving.