Preheat oven to 375 degrees F (190 degrees C).

Arrange the onions in a 9x13 inch baking pan. Arrange the onions so that the flat side of the onion is facing the ceiling.

In a small mixing bowl mix together the vinegar and sugar. Spoon the mixture onto the flat surface of the onions.

In another mixing bowl combine the breadcrumbs with 1/4 cup oil, sage, rosemary and parsley. Mix the mixture until well combined. Pat the mixture evenly onto the flat side of the onions.

Drizzle the remaining 1/4 cup of oil over the onions and bake for 45 minutes or until the onions are tender when pierced. Let the onions cool at room temperature. Serve with salt and pepper to taste.