In a large pot, bring 12 cups of water to a boil with the salt. Cook the pasta as per the package directions, then drain and let cool.
PREPARE THE BACON:
Lay the bacon in an unheated large pot (no oil needed) over medium-high heat. Cook for 3 minutes until golden, then turn and cook the other side for 2 minutes or until golden. Place on a paper towel-lined plate then chop into ½-inch pieces. Discard the bacon fat in the pot.
COOK THE CHICKEN:
Sprinkle the chicken with salt and pepper. Using the same pot over medium-high, melt the butter. Cook the chicken for 4 minutes on each side, then transfer to a plate. Rest for 5 minutes and cut into ½-inch thick slices.
MAKE THE TUSCAN SAUCE:
Melt the butter in the same pot, still on medium-high heat. Add the garlic and cook for 20 seconds. Add the wine, stir, then simmer rapidly for 2 minutes or until mostly evaporated. Lower the heat to medium, add the flour and stir for 1 minute. Switch to a whisk. While whisking, slowly pour in the milk- the mixture will thicken. Once the flour and milk are combined, add the cream and chicken broth. Whisk until lump-free. Bring to a simmer and stir regularly with a wooden spoon for 4 to 5 minutes until the sauce is thick enough to coat the back of the wooden spoon.Stir in the onion and garlic powder, salt, pepper and ⅔ of both the Parmesan and mozzarella. Once the cheese melts, the sauce should be thick and creamy.
ASSEMBLE AND BAKE:
Stir in the spinach, chicken, sun-dried tomato, most of the bacon (reserve some for topping) and pasta. Pour into a 13x9-inch baking dish, sprinkle with the remaining Parmesan, followed by the mozzarella and bacon. Bake for 25 minutes or until the cheese is melted and golden.
SERVE:
Let the pasta dish stand for 5 minutes before serving. Garnish with parsley, if desired.