Combine the yogurt, lemon juice, garlic, oregano, paprika, salt, and pepper.
Coat the chicken thighs and marinate for at least 1 hour.
Heat a grill pan or skillet over medium-high.
Cook the chicken 5-6 minutes per side until charred and cooked through.
Rest, then slice into strips.
Fill warm pita with chicken, tomato, onion, and tzatziki.