Preheat oven to 300°F (150°C).

In a large skillet, heat olive oil over medium-high heat.

Add ground beef and Italian sausage to the skillet and brown, breaking the meat apart with a spoon.

Remove the meat mixture from the skillet using a slotted spoon, leaving the pan juices in the skillet.

Add chopped onions to the skillet and sauté in the remaining pan juices until softened.

Drain the sautéed onions and add them to the browned meat mixture.

Cook egg noodles according to package directions until al dente (about 5 minutes in slightly salted water).

Drain the cooked noodles and transfer them to a large baking dish or casserole dish.

Stir in the meat and onion mixture, tomatoes, salt, pepper, processed cheese, and drained mushroom pieces into the noodles.

Do not include the bread crumbs at this stage.

Sprinkle bread crumbs evenly over the top of the casserole.

Bake in the preheated oven for 3 hours, or until bubbly and heated through.