Season chicken breasts or thighs with salt and pepper, then sear them in olive oil in a large skillet until golden brown; remove the chicken and set aside. In the same skillet, sauté the chopped onion and minced garlic until softened, then add the drained and chopped sun-dried tomatoes, heavy cream, chicken broth, and Italian seasoning, bringing the mixture to a gentle simmer to allow the sauce to thicken slightly.

Return the seared chicken to the skillet, stirring in the grated Parmesan cheese and fresh spinach. Continue to cook until the spinach has wilted and the chicken is heated through and coated in the creamy sauce.