Place a skillet over medium-high heat and grease with olive oil. Listen to the sizzle as you add the onions and cook for 2 to 3 minutes or until they become tender while stirring occasionally. Then, add the garlic and let it sizzle for a minute.
Add beef, season with salt, and cook for 7-10 minutes or until meat turns brown.
Add Italian seasoning, tomato sauce, and diced tomatoes. Stir to combine everything and let the mixture simmer for 20 minutes while stirring rarely. Add mushrooms, bell peppers, and corn kernels, and stir for 3 to 4 minutes or until vegetables are soft.
Prepare the oven and preheat it to 350°F.
Half of the cheese mixture and cooked macaroni should be added to the meat sauce, mixed well, and transferred to the casserole.
Sprinkle the cheese mixture on the casserole and loosely cover it with aluminum foil. Place in the oven and bake for 15 minutes.
Once the casserole is ready, remove it from the oven and let it rest for 5 to 8 minutes. Then, serve and enjoy the comforting warmth of this hearty casserole!