Wash and pat dry the 4 chicken breast fillets. Combine 2 tablespoons olive oil, 2 tablespoons lime juice, 2 teaspoons oregano, salt, and pepper to make a marinade. Brush the marinade over the chicken fillets and refrigerate until ready to cook.
Heat a large skillet over medium-high heat. Fry the chicken for 6-8 minutes until the internal temperature reaches 74 °C (165 °F).
While the chicken cooks, toast the flatbread for 2-3 minutes until warm and lightly toasted. Cut into 4 quarters.
Core the avocado and cut into strips.
Slice the 2 tomatoes.
Brush each flatbread quarter with 1 teaspoon mayonnaise. Top with 1/4 of the avocado strips, 1 cooked chicken fillet (cut to fit if needed), and tomato slices. Season with coriander, salt, and pepper.