Using a serrated edge knife, split bread in half horizontally.
Cut avocado in half, remove seed and skin, cut flesh into slices.
Top bottom half with avocado, sprinkle with fetta, top with spinach and drizzle with olive oil and vinegar, season with salt and pepper.
Then place remaining bread on top and place under the sandwich grill.
Toast until hot and golden.
For a non-vegetarian option add prosciutto.
Serving Size 4