Prep the chicken. Season both sides of each chicken breast in Italian seasoning, salt, and pepper.
Sear the chicken. Heat 2 tablespoons of the oil in a large skillet over medium heat. Add the chicken and sear for 3 to 4 minutes on each side, until golden. Remove the chicken from the pan to a plate and set aside.
Cook the onions. In the same skillet, add another tablespoon of oil and the onion. Saute for 2 to 3 minutes, until the onion has softened.
Add the sun-dried tomatoes and garlic and saute another minute, until fragrant.
Add the spinach, and saute another minute, until just starting to wilt.
Add the heavy cream and parmesan cheese, stir together, and bring to a simmer.
Let it simmer. Place the chicken back in the skillet and cook until heated through, about 5 minutes.