Preheat the oven to 375°F and lightly grease a large baking dish.
Mix breadcrumbs, Parmesan, garlic, ground beef, egg, herbs, and seasonings, then shape into medium meatballs.
Toss potatoes and mushrooms with olive oil and seasoning in the baking dish.
Pour tomato sauce over the vegetables and place meatballs on top.
Cover with foil and bake for 35 minutes.
Uncover and bake 15 to 20 minutes more until meatballs are cooked through and potatoes are tender.
Rest briefly, garnish if desired, and serve hot.