Place a large skillet over medium-high heat. Cook the bacon until crispy, flipping once or twice, about 8 minutes. Remove to a paper towel-lined plate to drain. Once cooled, crumble into small pieces.
Add the butter to the same skillet with any leftover bacon grease. Then, add the onion slices and cook until the onions begin to brown, about 5 to 8 minutes.
Reduce the heat to medium and continue to cook for another 15 to 20 minutes until the onions have caramelized and are soft and golden brown.
While the onions are cooking, bring a large pot of water to a boil and season the water generously with salt.
Add the rotini to the water and cook according to package directions until al dente. Drain the pasta and immediately run under cold water to stop the cooking and cool it down.
Pour the pasta into a large mixing bowl. Add the bacon, caramelized onions, chicken, cheese, and roasted red peppers. Toss to combine.
Pour the dressing over the ingredients in the bowl. Gently mix until everything is well coated.
Cover the bowl and refrigerate until ready to serve (up to 6 hours ahead of time). You could serve this pasta salad as soon as everything is mixed if you don't mind things being warm.
Notes
You could save yourself a little cooking time by using 1/2 of a rotisserie chicken from the store for the chicken in this recipe. Just shred the meat and you're all set!