Preheat the oven to 350°F. Spray a 9x13-inch baking dish with non-stick cooking spray.

Cook spaghetti according to package directions. Rinse with cold water, drain, and return to the cooking pot.

Into a large saucepan over medium-high heat, add the butter. When the butter is melted, add the onion and mushrooms. Cook, stirring frequently for 3 minutes, until softened. Add the evaporated milk, cream of chicken substitute, cheddar cheese, Montreal Chicken seasoning, celery salt, sea salt, and ground black pepper. Stir to combine. Adjust seasoning to taste

Pour the sauce over the spaghetti. Toss to evenly distribute the sauce throughout. The mixture will be very soupy. Transfer the pasta to the prepared 9x13-inch baking dish. Sprinkle Colby-Jack cheese over the top.

Bake, uncovered for 40 minutes then serve hot.