California Avocado Flat Bread Sandwich Recipe - Delicious & Easy!

Ingredients

• 3/4 cup white wine vinegar, divided
• 1/2 tbsp finely chopped fresh garlic
• 1/2 tsp salt
• 1/2 tsp freshly ground black pepper
• 1 cup olive oil
• 2 cups chopped sweet onion
• 2 cups chopped sun-dried tomato
• 24 rounds flat bread, such as pita - about 7 inches in diameter
• hearts of romaine leaves - as needed
• 3 cups romano cheese, grated
• 12 california avocados