Mix together all the ingredients for the Tzatziki sauce. Mix well and refrigerate until ready to serve.
Preheat the oven to 450 degrees. Spray both sides of pitas with olive oil. Arrange them in a single layer on a baking sheet and bake for 5 minutes.
In a small bowl combine the olive oil, vinegar, oregano, and garlic. Mix in the salt and pepper. Toss with the olives, onions, and sun dried tomatoes.
Spread 2 tablespoons of the hummus over each pita. Sprinkle with 2 tablespoons of mozzarella.
Divide the vegetable mixture evenly over the cheese and then sprinkle with the feta.
Cook the pizzas for 6 minutes. Remove from the over and serve with tzatziki sauce.