Preheat oven to 350°.
Remove white papery skin from garlic head (do not peel or separate the cloves). Wrap garlic head in foil. Bake at 350° for 1 hour; cool 10 minutes. Separate cloves; squeeze to extract garlic pulp. Set half of garlic pulp aside; reserve remaining garlic pulp for another use. Discard skins.
Heat a large Dutch oven over medium-high heat. Add pancetta; sauté 5 minutes or until crisp. Remove pancetta from pan, reserving drippings in pan. Add onion and 1 tablespoon oil to drippings in pan; sauté 5 minutes. Reduce heat to medium-low; cook 25 minutes or until onion is very tender and browned, stirring frequently. Stir in vinegar.
Preheat oven to 375°.
Add garlic pulp, pancetta, squash, and next 6 ingredients (through bay leaf) to onion mixture, stirring well. Place bread in a food processor, and pulse 10 times or until coarse crumbs measure about 1 cup. Combine breadcrumbs, Parmesan cheese, and 1/2 teaspoon olive oil; sprinkle evenly over squash mixture. Cover and bake at 375° for 50 minutes or until squash is tender. Uncover and bake an additional 15 minutes or until topping is browned. Discard bay leaf. Sprinkle with parsley.