Melt butter in a large sauté pan over medium heat. Add onion, garlic and chili flakes and cook 5 minutes, until onion is golden. Add salmon and tomato. Add salt and pepper to taste.
Increase heat to high and cook 2 minutes, stirring constantly. Pour in vodka, reduce heat and simmer until liquid is reduced by half. Add cream and continue to simmer until reduced again by half.
Meanwhile, cook fettuccine in a large pot of boiling salted water, until al dente. Drain and place in a warm serving bowl. Add sauce and toss to coat evenly. Sprinkle with parmesan cheese and garnish with fresh parsley.