Preheat oven to 350°F.
Cook macaroni according to package instructions; drain.
In a large mixing bowl, combine cooked macaroni, drained salmon, minced onion, parsley, cream of mushroom soup, evaporated milk, Parmesan, and grated cheddar cheese. Mix well to ensure even distribution of ingredients.
Grease a 13 x 9-inch baking dish with nonstick cooking spray. Pour the salmon mixture into the dish.
Mix melted butter with crushed crackers and sprinkle evenly on top of the casserole.
Bake in the preheated oven for approximately 35-45 minutes, or until the casserole is lightly browned and bubbling. Sprinkle with fresh parsley as a garnish.