01 - Generously season both sides of each chicken breast with salt and black pepper, pressing the seasoning into the meat to ensure adherence.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add chicken breasts and sear for 5 to 6 minutes per side until golden brown and cooked through to an internal temperature of 165°F. Transfer chicken to a clean plate and tent with foil to retain moisture.
03 - Reduce heat to medium. Add chopped onion to the same skillet and sauté for 2 to 3 minutes until translucent and softened. Add minced garlic and cook for 1 minute until fragrant, being careful not to brown the garlic.
04 - Stir in the sliced sundried tomatoes and cook for 1 minute to release their oils and infuse the pan with flavor.
05 - Pour in the chicken broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan. Reduce heat to medium-low and let the broth simmer for 1 minute to reduce slightly.
06 - Add heavy cream, grated Parmesan cheese, Italian seasoning, and crushed red pepper flakes. Stir continuously until the cheese melts and the sauce becomes smooth and velvety. Allow to simmer for 2 to 3 minutes until slightly thickened.
07 - Add fresh baby spinach to the sauce in batches, stirring until each batch wilts before adding more. Cook for approximately 2 minutes until all spinach is tender and incorporated.
08 - Return the seared chicken breasts to the skillet, nestling them into the sauce. Simmer for 3 to 4 minutes over low heat until the chicken is heated through and the flavors have melded together.
09 - Remove skillet from heat. Sprinkle chopped fresh parsley over the top as a garnish. Serve immediately while hot, accompanied by your choice of pasta, rice, or mashed potatoes.