To prepare the tzatziki dressing pour any liquid off the surface of the greek yogurt. (I find it is best to use full fat greek yogurt for this, but 2% works ok as well. You want the yogurt to be thick, so if your greek yogurt seems thin strain it through a fine mesh strainer). Mix together the greek yogurt, diced cucumber, garlic, white wine vinegar, dill, oregano, salt and pepper to taste, and lemon juice. Drizzle with olive oil. Place in the fridge while you bake the puff pastry.
Preheat the oven to 400 degrees F. Line 2 baking sheets with parchment paper.
Place the pastry on the prepared baking sheets. Using the tines of a fork, prick the top of the pastry all over. Cover the pastry with parchment paper and place another baking sheet on top. Bake for 25 minutes until golden. Remove the top baking sheet and parchment paper. Set aside.
While the puff pastry is baking combine the tuna (if there is a lot of oil in the can drain some of it off. I left about a tablespoon of oil. I think it helps add flavor and keep things moist), sun-dried tomatoes, kalamata olives and garlic and mix to break up the tuna and combine the ingredients. Add the red wine vinegar, greek yogurt, dill, oregano and parsley. Mix to fully combine.
To assemble the Napoleons: Place 4 pieces pastry on a work surface. Spread each piece with a little tzatiziki and a sprinkle of feta (I actually ended up mixing the feta into the tzatiziki), Cover that with spinach and then a layer of the tuna mixture. and top with a few slices of avocado. Place another sheet of puff pastry on top and then repeat the layering process. You should end with with three sheets of puff pastry for each napoleon.