Cook macaroni according to package directions; drain and set aside.
Heat the oil in a large skillet with a tight-fitting lid over medium-high heat until hot.
Add mushrooms, onion and bell pepper; cook and stir until onions and mushrooms are nicely browned, about 10 minutes; remove from skillet.
Add sausage to the skillet; using a fork to crumble the meat, stir-fry until browned, about 5 minutes.
Drain fat and blot remaining grease with paper towels (this technique will save you a lot of fat grams NOT reflected in the nutritional info below).
Return mushroom mixture to the skillet. Stir in tomatoes, tomato sauce, and cooked macaroni. Bring mixture to a boil then reduce heat to medium-low and simmer for 10 minutes, stirring occasionally.
Sprinkle with shredded Cheddar cheese; cover and simmer until cheese melts, about 5 minutes.