Season chicken on both sides with Italian seasoning, garlic powder, salt, and pepper. Heat olive oil in a large skillet over medium-high heat. Sear chicken 4-5 minutes per side until golden brown and cooked through (165°F). Remove and set aside.
Reduce heat to medium. Add butter to the same skillet. Add diced onion and cook 3 minutes until softened. Add garlic and sun-dried tomatoes, cook 1 minute until fragrant.
Pour in chicken broth, scraping up browned bits from the bottom of the pan. Add heavy cream and bring to a gentle simmer. Cook 3-4 minutes until the sauce starts to thicken.
Stir in grated Parmesan until melted and smooth. Add baby spinach and red pepper flakes. Stir until spinach is just wilted, about 2 minutes.
Return the chicken to the skillet. Spoon sauce over the chicken and simmer 2-3 minutes until heated through.
Serve over fettuccine, penne, or rice. Top with fresh basil and extra Parmesan.