Bring a large pot of water to a boil over high heat. Add 1 Tbsp salt and pasta. Cook pasta according to package directions for al dente. Reserve 1/4 cup pasta water and then drain pasta.
In a large skillet, heat olive oil over medium heat. Add garlic and lemon zest. Cook for 1 minute. Stir in Italian seasoning and crushed red pepper and cook for an additional minute.
Add butter to pan and, once melted, add baby spinach, pasta, reserved pasta water and lemon juice. Once spinach begins to wilt, stir in Parmesan cheese. Serve immediately.