Preheat an oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the macaroni, and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 8 minutes. Drain well in a colander set in the sink. Transfer to a large bowl. Stir the softened butter into the macaroni.
Heat the olive oil in a skillet over medium heat; cook the onion in the oil until brown, about 5 minutes. Stir in the salmon and seafood seasoning and cook until warmed through, about 5 minutes more. Remove from heat and pour the red wine vinegar into the skillet and set aside to cool.
Mix together the Cheddar cheese, eggs, milk, and vegetable stock in a large mixing bowl. Add the salmon mixture, peas and carrots, and corn; mix. Stir in the macaroni. Season with salt and pepper. Spread into the bottom of the prepared baking dish.
Toast the bread and break into small pieces. Combine the toasted bread and Parmesan cheese in a food processor; blend until chopped into crumbs. Sprinkle over top of the dish.
Bake in the preheated oven until heated through, about 45 minutes. Allow to cool 15 to 20 minutes before serving.
