Bring a large pot of salted water to a rolling boil. Cook fettuccine according to package directions until al dente, 9 to 11 minutes. Reserve 1/4 cup pasta water before draining. Drain and set aside.

While pasta cooks, pat salmon fillets completely dry with paper towels. Season both sides generously with salt and pepper.

Heat olive oil in a large skillet over medium-high heat until shimmering. Add salmon and cook for 3 to 4 minutes without moving. Flip and cook another 3 to 4 minutes until internal temperature reaches 145 degrees F and fish flakes easily. Transfer to a plate and flake into pieces.

In the same skillet over medium heat, add minced garlic and saute for 30 seconds until fragrant but not browned. Pour in heavy cream and bring to a gentle simmer. Cook for 2 to 3 minutes, stirring occasionally, until sauce thickens and coats the back of a spoon.

Stir in lemon juice and freshly grated parmesan. Whisk until cheese melts completely into the sauce. Season with salt and pepper. Add reserved pasta water a splash at a time if sauce is too thick.

Add cooked fettuccine and flaked salmon to the skillet. Toss gently to coat in the cream sauce. Cook for 1 minute to heat through. Remove from heat, top with fresh dill or parsley, and serve immediately.