INGREDIENTS
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1 large Spanish onion or Vidalia , thinly sliced (about 2 cups)
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2 tablespoons olive oil
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8 plum tomato, cut in half lengthwise
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1/2 of a 17.3-ounce package Puff Pastry Sheets(1 sheet), thawed
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2 tablespoons Dijon-style mustard
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1 cup shredded mozzarella cheese(about 4 ounces)
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1 tablespoon chopped fresh oregano leaves