Cook the Pasta: Boil salted water and cook rotini until al dente (8-10 minutes). Drain, rinse with cold water, and let cool.
Prep the Ingredients: Dice the chicken, crumble the bacon, halve the tomatoes, and chop the cucumber, red onion, and lettuce.
Make the Dressing: Whisk together mayonnaise, ranch dressing, Dijon mustard, garlic powder, salt, and pepper until smooth.
Assemble the Salad: In a large bowl, mix the cooled pasta, chicken, bacon, tomatoes, lettuce, cucumber, cheese, and red onion.
Toss with Dressing: Pour the dressing over the salad and toss until evenly coated.
Chill and Serve: Cover and refrigerate for 30 minutes, then serve chilled.