Toss the sliced chicken with the olive oil and fajita seasoning until evenly coated.
Heat a large frying pan over medium-high heat. Add the chicken and cook for 5–7 minutes, turning occasionally, until browned and cooked through. Remove from the pan and set aside.
Add the sliced onion and capsicum to the same pan. Cook for 5–6 minutes, stirring occasionally, until tender-crisp.
Return the cooked chicken to the pan and toss with the vegetables until heated through and well combined.
In a small bowl, mix the Greek yoghurt, lime juice and a pinch of garlic powder.
Warm the tortillas in a dry frying pan or microwave until soft and pliable.
Fill each tortilla with shredded lettuce, the chicken and vegetable mixture, avocado and a dollop of yoghurt lime sauce. Serve with lime wedges. Enjoy!