Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, minced onion, milk, egg, garlic powder, salt, pepper, and oregano. Mix until well combined.
Roll the mixture into golf ball-sized meatballs and place them on the prepared baking sheet. You should have about 16 meatballs.
Bake the meatballs in the preheated oven for 15-20 minutes, or until they are cooked through and reach an internal temperature of 160°F (71°C).
While the meatballs are baking, heat olive oil in a medium skillet over medium heat. Add the sliced mushrooms and sauté for about 5 minutes until browned.
Sprinkle the flour over the mushrooms and stir to combine. Gradually add beef broth while stirring to avoid lumps. Bring to a simmer.
Once the gravy thickens, stir in the heavy cream, soy sauce, and Worcestershire sauce. Allow it to simmer for another 5 minutes. Season with salt and pepper to taste.
When the meatballs are done baking, add them to the mushroom gravy in the saucepan, and gently toss to coat the meatballs in the sauce. Allow them to simmer together for 5 more minutes.
Serve warm over mashed potatoes or rice, and enjoy your Ultimate Smothered Meatballs!