Preheat the oven to 375°F and lightly grease an 8-inch baking dish. Heat the olive oil in a large skillet over medium heat and sauté the onion and mushrooms until the onion is translucent. Meanwhile, boil the egg noodles until al dente, about 7 minutes.
Add the cream of mushroom soup, cream cheese, sour cream, milk, and garlic powder to the skillet. Heat until smooth and hot, then season with salt and black pepper.
Drain the noodles well, add them to the skillet, and stir until evenly coated in the sauce.
Fold in the drained tuna, transfer the mixture to the prepared baking dish, and spread it evenly.
Top with the shredded Colby Jack, followed by the French fried onions.
Bake at 375°F for 10 minutes, until the onions are golden and the filling is hot. Serve immediately.
Notes
Recipe facts extracted from the source Recipe JSON-LD; the source offers chicken or turkey as alternatives, while this canonical blueprint follows the primary tuna version.