In a bowl, mix olive oil, lemon juice, garlic, oregano, paprika, salt, and black pepper.
Add chicken and coat well. Marinate for 15–30 minutes if possible.
Heat a skillet over medium heat and cook chicken for 5–7 minutes per side until fully cooked.
Let the chicken rest for a few minutes, then slice or chop into pieces.
Grate the cucumber and squeeze out excess water.
In a bowl, mix Greek yogurt, cucumber, olive oil, lemon juice, garlic, salt, pepper, and dill (if using).
Warm pita bread in a dry skillet for 20–30 seconds per side.
Fill each pita with chicken, lettuce, tomatoes, and red onion.
Spoon tzatziki on top and add feta if desired. Serve immediately.