Step 1

Bring a large pot of water to a boil.

Step 2

Cook the peppers in boiling water until softened, 4 to 5 minutes.

Step 3

Remove peppers from boiling water and rinse with cold water; set peppers aside to drain.

Step 4

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.

Step 5

Preheat oven to 350 degrees F (175 degrees C).

Step 6

Divide beef and rice mixture among peppers; stuff each pepper with beef and rice mixture.

Step 7

Place peppers open side up in a 9x13-inch baking dish or shallow roasting pan.

Step 8

Combine tomato sauce and white vinegar in a bowl.

Step 9

Pour tomato mixture over stuffed peppers.

Step 10

Top with 2 tablespoons grated Parmesan cheese.

Step 11

Bake in the preheated oven until heated through, basting the peppers two or three times while baking, about 80 minutes.