Heat the oil in a large heavy pot or Dutch oven over medium-high heat Add the onions and mushrooms and cook until the onions are softened, 3 to 5 minutes. Add the ground meat and cook until no longer pink, about 3 minutes. Add the garlic, pasta, crushed tomatoes, and stock or water. Make sure the liquid covers everything.
If adding canned beans instead of meat, add them here. If adding raw chopped vegetables, add them here. If adding seafood, add it here.
Cover and cook medium-low heat (do not open) until the liquid is absorbed and the pasta is cooked, about 20 minutes. Stir to combine. (If adding frozen vegetables add during the last 5 minutes of cooking.)
If you lift the lid and it's too soupy, at the end of cooking, simply remove the lid and cook until the liquid has reduced and the pasta is cooked. Taste and adjust for seasoning with salt and pepper. Serve with grated Parmesan.