Start by bringing a large pot of salted water to a boil and cook the rigatoni pasta according to the package instructions. Once done, drain the pasta and set aside, reserving some pasta water.
Season the chicken breasts on all sides with olive oil, salt, black pepper, garlic powder, and Italian seasoning.
Heat a large skillet over medium-high heat. Cook the seasoned chicken breasts for about 5-6 minutes on each side or until they reach an internal temperature of 165 degrees. Transfer the cooked chicken to a cutting board and let it rest for a moment before chopping it into bite-sized pieces.
In the same skillet, add the butter, sliced mushrooms, and diced onions. Sauté them until they are halfway soft. Then, add the cherry tomatoes and continue cooking until the vegetables are tender, and the tomatoes have started to blister.
Stir in the minced garlic and spinach, cooking until the spinach wilts down. Add the chive and onion cream cheese and heavy cream. Cook until the sauce comes together, and the cream cheese melts. Reduce the heat to low.
Add the cooked rigatoni pasta, chopped chicken, freshly grated Parmesan cheese, and mozzarella cheese to the skillet. Toss everything to coat it evenly in the creamy sauce. If the sauce is too thick, gradually add a bit of the reserved pasta water until you reach your desired consistency.
Season the dish with salt, pepper, and garlic powder to taste.