Mix the vinegar, some olive oil, mustard and the chopped herbs together in a large bowl, add the chicken and mix to coat. Marinate for 1 hour - 24 hours
Heat oil in frying pan over medium heat. Add chicken and cook for 4-6 minutes on each side, or until cooked. Transfer to a plate and cover with foil to keep warm while resting. Turn heat up to medium high. Add oil if required.
Add onion and garlic, cook for 2 minutes. Add capsicum and cook for 1 minute or until onion is translucent. Add orzo, tomato, chicken stock, oregano, chili flakes, salt and pepper. Mix and bring to simmer, then lower heat to medium low or so it simmers gently.
Cook for 9 - 10 minutes, stirring frequently. Take it off the stove when the pasta is just cooked. Stir through parmesan and basil and spoon into serving bowls, top with sliced chicken and serve with extra parmesan and basil.