Preheat your oven to 425°F (220°C). Toss the cauliflower florets with olive oil, salt, and pepper on a baking sheet. Roast for 25-30 minutes, turning halfway through, until the cauliflower is golden and tender.
While the cauliflower roasts, bring a large pot of salted water to a boil. Add the ziti pasta and cook according to package instructions until al dente. Drain and set aside, reserving about 1/2 cup of the pasta water for later.
Transfer the roasted cauliflower to a blender or food processor. Add the vegetable broth, heavy cream, garlic powder, onion powder, nutmeg, and a pinch of salt and pepper. Blend until the sauce is completely smooth and creamy.
In a large skillet or saucepan, heat the blended cauliflower Alfredo sauce over medium heat. Stir in the grated Parmesan cheese until melted and incorporated. Add the shredded cooked chicken, then mix in the cooked ziti. Toss everything together, adding reserved pasta water a little at a time if you want to loosen the sauce.
Remove from heat and sprinkle the chopped fresh parsley over the top for a burst of color and freshness. Serve immediately.
