In a saucepan, melt the butter over medium heat. Add the onion and cook, stirring, until wilted, about 5 minutes. Stir in the flour and cook for a minute or two, then whisk in the milk. Cook, stirring constantly over medium heat, until the sauce begins to thicken and bubble. Dump in the frozen peas and cook until sauce returns to a simmer.
Now, open the can of salmon and drain the juice into the sauce. Stir until smooth. Pick through the salmon, removing skin and bones and whatever other gross bits your kids may find disgusting. Flake the salmon into large chunks and gently stir into the sauce along with the parsley and Parmesan. Remove from heat.
Cook the pasta in lots of boiling water until tender but not mushy. Drain thoroughly, then dump into a bowl. Add the sauce and toss gently to mix. Season to taste with salt and pepper.
Sorry, there is no nutrition information available for this recipe.