Bring a large pot of salted water to a rolling boil. Cook fettuccine until al dente according to package instructions (about 9 to 10 minutes). Reserve 1/2 cup of starchy pasta water, then drain pasta and set aside.
Pat raw shrimp thoroughly dry with paper towels. Season with Italian seasoning, 1/2 tsp salt, and black pepper.
Heat 1 tbsp olive oil and 1 tbsp butter in a 12-inch cast iron skillet over medium-high heat until hot. Add the shrimp in a single uncrowded layer. Sear for 1.5 to 2 minutes per side until pink, opaque, and lightly caramelized. Transfer shrimp to a clean plate immediately (do not overcook).
In the same skillet over medium heat, melt the remaining 1 tbsp butter with 1/2 tbsp olive oil. Add the minced garlic and sliced sun-dried tomatoes. Sautu00e9 for 1 minute until fragrant.
Pour in the seafood broth and heavy cream, scraping up the browned pan fond with a wooden spatula. Bring to a gentle simmer for 3 minutes until slightly thickened.
Stir in the grated Parmigiano-Reggiano, fresh lemon juice, and red pepper flakes. Whisk gently until the cheese completely melts into a silky, luscious cream sauce.
Add the fresh baby spinach and drained fettuccine into the sauce. Toss continuously for 1 to 2 minutes over low heat until the spinach wilts and the pasta is thoroughly coated with velvety sauce (add a splash of reserved pasta water if needed to loosen).
Fold the seared shrimp back into the skillet for 1 minute to warm through. Remove from heat.
Garnish with chopped fresh parsley, extra shaved parmesan ribbons, and charred lemon slices. Serve immediately hot with warm garlic ciabatta bread.