Combine chicken tenderloin chunks, olive oil, minced garlic, lemon juice, minced parsley, oregano, salt and pepper in a large ziploc bag. Seal then shake to coat. Let chicken marinate in the fridge for at least 30 minutes.
Meanwhile, prep your toppings.
When ready to cook, heat a large skillet over medium heat. Once the skillet is hot, add the contents of the chicken marinade ziploc bag. Arrange the chicken chunks in a single layer then cook until chicken is cooked through (internal temp 165F) and golden on the outside, about 10-15 minutes, stirring occasionally. Remove skillet from heat.
Warm the pitas in the microwave for about 1 minute. Fill each warm pita like a taco starting with the cooked chicken, then shredded lettuce, diced tomatoes, diced onion, diced cucumber, then a drizzle of tzatziki and finally some crumbled feta. Fold the pita up and enjoy!