Preheat a baking stone in the oven at 550 degrees.
Shape the dough into a ball by hand or using a rolling pin. Brush the top of the pizza dough with olive oil and sprinkle with oregano. Gently pierce the dough with a fork to prevent large air bubbles during cooking.
Remove the pizza stone from the oven and sprinkle the pizza stone (or cookie sheet) with cornmeal. Transfer the pizza to the stone. Cook for 7-8 minutes or until golden brown.
While the dough is baking, heat ½ tablespoon of extra virgin olive oil in a medium skillet over medium high heat. When the oil is hot, add in the chicken breast and season with ¼ teaspoon dried oregano, minced garlic, salt, and pepper. Cook about 3-4 minutes on each side, until the chicken is golden brown and fully cooked. Transfer the chicken from the pan to a cutting board and cut into bite size pieces.
Make the Tzatiki by combining the yogurt, shredded cucumber, lemon juice, garlic, and salt and pepper to taste in a bowl.
To assemble the pizza, place the desired quantity of Roma tomatoes, cucumber, avocado, feta cheese and chicken breast on the prepared crust. Drizzle with Homemade Tzatziki and serve additional sauce on the side for dipping.