Season the chicken. Generously sprinkle both sides of each chicken breast with Italian seasoning, salt, and black pepper.
A plate of chicken breasts seasoned for Tuscan chicken
Sear the chicken. In a large skillet over medium heat, warm 2 tablespoons of olive oil. Add the chicken and cook for 3 to 4 minutes per side, until a golden crust forms. Transfer the chicken to a plate and set it aside.
A skillet showing seared chicken breasts for Tuscan chicken
Sauté the onions. Using the same skillet, add the remaining tablespoon of oil along with the chopped onion. Cook for 2 to 3 minutes, stirring occasionally, until the onion becomes soft and translucent.
Cooking chopped onions in a skillet for Tuscan chicken
Add garlic and sun-dried tomatoes. Stir in the garlic and sun-dried tomatoes and cook for another minute, just until the mixture becomes fragrant.
Sun-dried tomatoes and garlic cooking together in the skillet
Add spinach. Toss in the baby spinach and cook for about a minute, just until it begins to wilt slightly.
Spinach wilting in the skillet with other ingredients
Pour in the cream and cheese. Add the heavy cream and freshly grated Parmesan cheese to the skillet, stirring well to combine. Bring the mixture to a gentle simmer.
Creamy Tuscan sauce coming together in the skillet
Simmer the chicken. Return the seared chicken breasts to the skillet, nestling them into the sauce. Let everything simmer together for about 5 minutes, or until the chicken is heated through and the sauce is slightly thickened.