Roast the Cauliflower: Toss the cauliflower florets with olive oil, salt, and pepper. Roast at 400°F (200°C) for 15–20 minutes until tender and slightly browned. Let it cool.Mix the Dressing: In a small bowl, whisk together the mayonnaise, fresh dill, lemon juice, minced garlic, and Dijon mustard.
Combine: In a large mixing bowl, combine the shredded chicken, cooled cauliflower, diced red pepper, and celery.Toss: Pour the dressing over the chicken and vegetable mixture. Toss gently until everything is evenly coated.
Serve: Season with extra salt and pepper to taste, or serve chilled over a bed of mixed greens.