In a mixing bowl, whisk together olive oil, freshly squeezed lemon juice, minced garlic, oregano, paprika, salt, pepper, and red pepper flakes until well combined.

Add chicken breast chunks and toss gently to coat. Cover with plastic wrap and marinate for at least 15 minutes.

Chop cucumbers, tomatoes, bell pepper, and red onion into bite-sized pieces.

Combine with feta cheese and parsley in a separate bowl. Squeeze in additional lemon juice, season with salt and pepper, and let sit.

Heat a skillet over medium-high heat, add the marinated chicken in a single layer and cook for 3-5 minutes.

Flip and continue cooking until the chicken reaches an internal temperature of 165°F, about another 3-4 minutes.

Heat pitas until warm and pliable, either over an open flame, in a skillet, or in a preheated oven at 350°F for about 5-7 minutes.

Fill warm pitas with cooked chicken, spoon fresh salsa on top, and drizzle with tzatziki sauce.