1. In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, egg, garlic, oregano, salt, and pepper. Mix until just combined, being careful not to overwork the meat.
2. Form the mixture into small meatballs, about the size of a walnut.
3. Heat olive oil in a skillet over medium-high heat. Brown the meatballs on all sides, about 5 minutes, then transfer them to the slow cooker.
4. In the same skillet, add sliced onions and cook until they are soft and translucent, about 5 minutes. Add to the slow cooker.
5. Pour beef broth and Worcestershire sauce over the meatballs and onions in the slow cooker.
6. Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the meatballs are cooked through and tender.
7. About 30 minutes before serving, add the cornstarch mixture to the slow cooker and stir gently. This will thicken the gravy as it cooks.
8. Garnish with fresh parsley before serving.

This method lets the slowcooker do most of the work, much like my grandmother’s long-simmering soups. The preparation is straightforward, and the result is a dish brimming with flavor. Feel free to adjust the cooking time based on your schedule — a longer cook will only deepen the flavors.