Pat the chicken breasts dry and season both sides with Italian seasoning, salt, and pepper.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Place the chicken in the skillet and cook for 4-5 minutes per side, until golden brown. The chicken does not need to be fully cooked. Transfer the chicken to a plate.
Reduce the heat to medium. Add the remaining 1 tablespoon of olive oil to the same skillet. Add the chopped onion and cook for 2-3 minutes, until softened.
Stir in the minced garlic and sliced sun-dried tomatoes. Cook for 1 minute until the garlic is fragrant.
Add the baby spinach to the pan in handfuls, stirring until it just begins to wilt, about 1-2 minutes.
Pour in the heavy cream and sprinkle in the Parmesan cheese. Stir to combine and bring the sauce to a gentle simmer. Scrape up any browned bits from the bottom of the pan.
Return the chicken breasts and any accumulated juices to the skillet. Reduce the heat to low, cover, and let simmer for 5-7 minutes, or until the chicken is cooked through.
Confirm the chicken has reached a safe internal temperature of 165°F (74°C) with an instant-read thermometer. Serve immediately, spooning extra sauce over the chicken.