Bring a large pot of water to a boil, add salt, and cook the pasta until just al dente. Before draining, reserve ½ cup of pasta water.
Pat the chicken strips dry, season, and heat olive oil and butter in a skillet. Sear the chicken for 4-5 minutes per side until golden and cooked through.
In the same skillet, cook diced onion until translucent, add garlic and sun-dried tomatoes. Cook until fragrant.
Deglaze the pan with chicken broth, then add heavy cream, remaining Italian seasoning, and red pepper flakes. Simmer until the sauce thickens.
Lower the heat, gradually stir in Parmesan until melted, then add spinach and let it wilt.
Return chicken and pasta to the skillet, toss to combine, and add reserved pasta water as needed for sauce consistency.
Serve topped with fresh basil, extra Parmesan, and a squeeze of lemon if desired.
