Cook the pasta according to package instructions and set aside.
Meanwhile, heat 1 tablespoon of the olive oil and the butter in a large skillet over medium heat. Once the pan is hot, add the chicken pieces and season with salt and pepper.
Cook until browned and no longer pink inside, about 10 minutes, stirring occasionally. Transfer the cooked chicken to a plate and set aside.
Reduce the heat to medium-low and add another tablespoon of olive oil. Add the onions and sauté until softened, about 4-5 minutes. Add the minced garlic and stir for another minute.
Then, stir in the cream cheese and reduce the heat to low. Add the Greek yogurt, milk, and parmesan cheese and stir well to combine. Add the spinach, tomatoes, basil, chili flakes (if using) and stir again.
Finally, add the cooked chicken and penne to the creamy mixture and stir everything well to coat.
Next, heat the oven to 375° and grease a 9 x 9 or 9 x 13 dish.
Then, pour in the penne mixture and top with the shredded marble cheese.
Bake for 20 minutes. If you like a crustier cheesy top, turn on the broiler and broil the pasta for 2 minutes or so to get that nice browned top.
Serve hot.