If you're using Better Than Bouillon, add it to a sauce pan with some water and give it a quick stir to combine. If your tomatoes are especially juicy, you might be able to use their juice and skip the water, but mine were not.
Add tomatoes, onions, and oil or butter. Stir. Sprinkle the mushrooms on top and cover the sauce pan. Allow it to cook for at least 45 minutes.
Remove the lid and stir. It should smell delicious at this point but probably needs to cook down for a few minutes. If that's the case, leave the lid off, increase the heat a bit, and let it steam off some of the excess liquid while you boil your pasta.
Once it thickens, taste the sauce. Season with salt and pepper if you need more flavor. Mine didn't.
Ladle a good amount of the tomatoes, onions, and mushrooms into a bowl, along with a lot of the liquid. Place cooked pasta on top and spoon more of the sauce over it. Add cheese if you eat it and gently combine.