Heat olive oil in a large pan over medium heat. Season chicken with salt and pepper, then cook for 3–5 minutes per side until fully cooked. Remove and set aside.
In the same pan, add butter, onions, garlic, and crushed red pepper. Sauté for 1–2 minutes until fragrant.
Pour in heavy cream and chicken broth. Add sun-dried tomatoes and cream cheese. Simmer and whisk until smooth.
Stir in Parmesan cheese and spinach. Cook until spinach wilts and sauce thickens.
Return chicken to the pan and coat with the sauce. Simmer briefly until heated through.
Garnish with basil and serve your One-Pan Creamy Chicken and Spinach over pasta or cauliflower rice.