Preheat the oven to 400 degrees F. Line a rimmed baking sheet with parchment paper.

To make the meatballs, in a large bowl, combine the beef, breadcrumbs, milk, green onions, eggs, salt and pepper. Mix until all ingredients are well-blended. Scoop two tablespoons of the meat and form into balls. Arrange the meatballs onto the prepared sheet pan. Bake the meatballs until lightly browned and cooked through, about 20 to 25 minutes.

To prepare the mushroom gravy, heat the oil in a large skillet over medium heat. Add the garlic and shallot and cook until shallot has started to soften, about 2 minutes.

Add the mushrooms and cook for 2 to 3 minutes, or until soft and brown. Reduce heat to medium, add the butter and once melted, whisk in the flour until completely dissolved.

Gradually whisk in the broth. Continue whisking until the mixture is mostly lump free. Whisk in the water, mustard and Worcestershire sauce. Bring the mixture to a boil. Season to taste with salt and pepper.

Add the meatballs to the gravy in the skillet and simmer for 5 minutes or until the sauce has thickened and the meatballs have fully absorbed the sauce.

Serve over rice or on their own.