Preheat oven to 350°F. Lightly grease a small baking sheet. Season salmon with coriander, salt, and pepper. Roast on prepared baking sheet until cooked through, 13 to 15 minutes. 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 tablespoons butter in a large skillet over medium heat. Add onion and season with salt and pepper. Cook, stirring occasionally, until tender, 6 to 8 minutes. Add wine and cook until syrupy, 3 to 4 minutes. Add pasta and 1/2 cup reserve cooking water. Bring to a simmer. Remove from heat and stir in remaining 2 tablespoons butter (adding additional cooking water if needed to create a sauce). Gently fold in dill and salmon.