Preheat an oven to 180 degrees C. 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 egg noodles and return to a boil. Cook the noodles uncovered, stirring occasionally, until cooked through, but still firm to the bite, about 5 minutes. Drain well in a colander set in the sink.
While the noodles are cooking, stir the tuna, condensed soup, peas with mushrooms and onions, onion, milk, salt and pepper in a bowl until evenly mixed. Gently stir in the cooked pasta, then pour the mixture into a 20x30cm baking dish. Sprinkle evenly with dry bread crumbs.
Bake in the preheated oven until the casserole is bubbling and the bread crumbs are golden brown, about 20 minutes.