In a large skillet add olive oil over medium-high heat.
Once the oil is hot add in the ground beef, mushrooms, yellow onion, and garlic.
Cook until the meat is browned and the mushrooms and onions are soft.
Add meat mixture to a large slow cooker and add in the remaining ingredients.
Stir to combine and cook on low heat for 8-10 hours.
If the mixture gets too thick while cooking you can thin it out with a little more tomato sauce, stock, or wine.
Remove the bay leaves before serving over pasta or with garlic bread.