Baked Spaghetti Casserole

Begin by filling a large container with salted water and placing it on the stovetop to reach its boiling point. Next, carefully add the spaghetti into the pot and cook for 8-10 minutes, or until it reaches a firm yet slightly yielding texture. Remove the spaghetti from the water using a strainer, and set it aside.

In a large pan over medium-high heat, sauté the onions, green peppers, and ground beef until the meat is browned and the vegetables are tender. Once this process is complete, add the tomatoes, mushrooms, and oregano to the pan and continue cooking for another 10 minutes.

Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). Grease a 9x13 inch baking dish with cooking spray. Then, place half of the cooked spaghetti into the prepared dish. Top this layer with half of the meat mixture, followed by half a cup of mild Cheddar cheese. Repeat this process to create a second layer.

In a separate bowl, combine the cream of mushroom soup and water until smooth. Pour this mixture over the casserole. Finally, sprinkle a layer of Parmesan cheese on top.

Place the dish in the preheated oven and bake for 30-35 minutes. Remove it from the oven after this time, let it rest for 10 minutes before serving.