Preheat your oven to 375°F (190°C).

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the diced white onion and sliced Bella mushrooms. Sauté until the onions are translucent, about 5-7 minutes.

While vegetables are sautéing, bring a pot of salted water to boil. Cook 12 ounces of egg noodles according to package instructions, about 6-8 minutes. Drain and set aside.

In the same skillet, lower the heat and add 8 ounces of cream cheese, 1 cup of sour cream, 1 can of cream of mushroom soup, and ½ cup of milk. Stir until well combined and heated through, seasoning with salt and pepper.

In a mixing bowl, combine cooked egg noodles, 2 cans of drained tuna, and 1 ½ cups of colby jack cheese with the sauce mixture. Stir gently to coat.

Grease a 9x13-inch baking dish and pour the tuna mixture into it, spreading evenly.

Sprinkle 1 cup of French fried onions evenly on top.

Bake in the preheated oven for 10-15 minutes until the topping is golden brown and the casserole is bubbly.

Remove from the oven and let cool for 5 minutes before serving.