Heat oven to 400°F. Pat salmon dry; rub with oil, its salt, and pepper. Roast on lined sheet 10 to 15 minutes to 145°F in thickest center.
Meanwhile, cook tagliatelle with tablespoon salt to 1 minute short of package time. Reserve 1 cup pasta water; drain.
Melt butter in large skillet over low; add cream, milk, and zest. Gently simmer 2 minutes. Add pasta and 1/4 cup reserved water; toss 1 to 2 minutes until tender.
Remove from heat; gradually add Parmesan, loosening with water if needed. Rest salmon 2 minutes; flake portions into broad pieces.
Divide pasta among bowls; top with salmon. Spoon only a little sauce around fish to keep pieces intact.