Spray a large non-stick frying pan with olive oil and set over medium-high heat. Cook chicken thigh for 1 minute each side, or until fillets are golden.
Add the onion, garlic and capsicum to the pan and stir fry for 1-2 minutes, or until just softened.
Add olives, diced tomatoes, white wine, dried oregano, rosemary, chicken stock and mushrooms. Bring to the boil, then reduce heat to low and simmer for 10-15 minutes, or until chicken is cooked right through. Meanwhile, cook couscous according to packet instructions.
To serve, divide ½ cup cooked couscous between plates and spoon chicken mixture over the top.