Homestyle Stuffed Peppers

Bring a large pot of water to a boil.
Cook the peppers in boiling water until softened, 4 to 5 minutes.
Remove peppers from boiling water and rinse with cold water; set peppers aside to drain.
Mix together ground beef, cooked white rice, lightly beaten egg, finely chopped onion, Italian-style bread crumbs, salt, black pepper, garlic powder, and 1/4 cup grated Parmesan cheese in a large bowl until evenly mixed.
Preheat oven to 350 degrees F (175 degrees C).
Divide beef and rice mixture among peppers; stuff each pepper with beef and rice mixture.
Place peppers open side up in a 9x13-inch baking dish or shallow roasting pan.
Combine tomato sauce and white vinegar in a bowl.
Pour tomato mixture over stuffed peppers.
Top with 2 tablespoons grated Parmesan cheese.
Bake in the preheated oven until heated through, basting the peppers two or three times while baking, about 80 minutes.