Start by setting all your ingredients out. This dinner is quick to make so you need everything handy.
Grate the parmesan according to story notes. Set aside.
Boil water with salt and olive oil. Cook pasta. Drain. Drizzle with olive oil and toss so it doesn't stick, and just set it aside.
Seafood: In medium skillet on medium heat, add olive oil, butter, garlic, lemon juice, lemon peel, salt, and pepper. Let melt and simmer until fragrant (2-3 minutes).
Add all defrosted seafood. Simmer until shrimp is pink. Remove from heat and set aside. Do not overcook.
Alfredo Sauce: In large skillet over medium heat, add olive oil, butter, and diced onion. Cook 3-4 minutes until onions are translucent. Add garlic and cook another 1-2 minutes until fragrant. (Do not scorch garlic.)
Add flour and whisk vigorously 1-2 minutes. It will thicken just to spread apart when whisk goes through but go right back together.
Add heavy cream, milk, Italian seasoning, lemon peel, salt, and pepper. Whisk while cooking another 3-5 minutes until it starts to thicken. Remove from heat.
Add the more roughly grated half of the parmesan cheese wedge. Continue whisking vigorously until melted and smooth. It will be very thick.
Get seafood mix that you set aside before and add to the cream sauce, including the juices. This will thin the sauce back out to a nice rich, but not too thick, consistency. Stir well. Put back on medium-low heat a few minutes to ensure it's heated through, stirring the whole time. Then remove from heat.
Plating: Add mound of pasta to plate. Ladle seafood Alfredo sauce over pasta. Top generously with finely grated parmesan cheese. Serve with side of garlic bread.
