To make the dressing, in a small bowl, whisk together mayonnaise, lemon juice, Parmesan cheese, brown mustard, Worcestershire sauce, and salt and pepper to taste (I like 1/2 teaspoon salt and 1/4 teaspoon pepper). Cover and refrigerate while preparing the rest of the salad.
In a large saucepan or stock pot, bring 4 quarts water and 1 tablespoon salt to a boil. Add rotini and cook according to package instructions, about 9 to 11 minutes. Drain and rinse with cold water.
Meanwhile, arrange chicken on a baking sheet or work surface and sprinkle both sides generously with Cajun seasoning. In large skillet, heat oil until shimmering. Arrange chicken in a single layer and cook, flipping once, until the temperature on an internal thermometer reaches 165 degrees, about 5 minutes on each side. Remove from heat and rest for 5 minutes. Slice into strips.
In a very large bowl, combine cooled rotini, lettuce, croutons, and bacon. Drizzle with Caesar salad dressing and toss until uniformly coated. Top with chicken and garnish with Parmesan cheese.