In a bowl, whisk together olive oil, lemon juice, minced garlic, oregano, paprika, salt, pepper, and red pepper flakes. Add the chicken to the marinade.

Cover and let the chicken marinate for at least 15 minutes, or up to 45 minutes for more flavor.

While the chicken marinates, prepare the salsa by chopping the cucumber, tomatoes, bell pepper, and red onion, then combining them in a bowl with parsley and feta cheese.

Heat a skillet over medium-high heat, add the marinated chicken, and cook for about 3-5 minutes per side until cooked through.

Warm the pitas over a flame or in a dry skillet.

Assemble by placing chicken in each pita, topping with salsa and tzatziki sauce.