Preheat the oven to 425°F. Melt 2 tablespoons of butter in a large pot over medium heat. Add the onion, the chicken, and season with salt and pepper. Then aAdd 2 tablespoons of butter, the green onions, thyme, paprika, garlic powder, and cayenne, and cook until golden and toasted, 2-3 minutes.Add the broth and milk. Bring to a gentle boil over medium heat. Add the pasta and zucchini, and season with salt and pepper. Stir frequently until the pasta is al dente and the broth has been absorbed, about 8 minutes. Stir in the parmesan and 1 cup of shredded cheese. If needed, transfer everything to an oven-safe casserole dish. Scatter the remaining cheese over the top of the casserole. Bake 20 minutes, until the cheese is melted and beginning to brown. Serve warm, with additional thyme and fresh basil.