Drain the jar of sun-dried tomatoes, reserving the oil. Set the tomatoes aside and slice them if desired.
Toss the cubed chicken with 1 teaspoon Italian seasoning, salt, paprika, red pepper flakes, and black pepper until evenly coated.
Heat a skillet over medium heat and add the reserved sun-dried tomato oil. Add the seasoned chicken and cook, stirring occasionally, until browned and cooked through, about 6–8 minutes.
Sprinkle 1/4 cup grated Parmesan over the cooked chicken, then remove the chicken from the pan and set aside.
Add butter to the same skillet. Sauté the diced onion and minced garlic over medium heat until the onion is tender, about 5 minutes.
Stir in the remaining 1 teaspoon Italian seasoning, then add the water, heavy whipping cream, and uncooked pasta to the skillet.
Bring the mixture to a rapid simmer over medium-high heat and cook, stirring occasionally, until the pasta is tender, about 8–12 minutes.
Reduce the heat to low and stir in the spinach, cooked chicken, and sliced sun-dried tomatoes. Cook until warmed through and spinach is wilted.
Sprinkle shredded Parmesan cheese over the pasta and serve immediately.