Preheat oven to 350°F. Lightly grease small baking sheet. Season salmon with coriander, salt & pepper. Roast until cooked through, 13-15 min. Transfer to a plate. Cool completely, then flake into large pieces.
Meanwhile, cook pasta according to package directions, adding peas during last 1 (if using frozen) to 4 (if using fresh) minutes. Reserve 1 cup cooking water; drain. Return pasta to pot.
Melt 2 T butter in a large skillet over medium heat. Add onion, season with salt & pepper. Cook, stirring occasionally, until tender, 6-8 min. Add wine &cook until syrupy, 3-4 min. Add pasta & 1/2 C reserve cooking water. Bring to simmer. Remove from heat & stir in remaining 2 T butter (adding additional cooking water if needed to create a sauce). Gently fold in dill & salmon.