Preheat oven to 180°C. Heat the oil in a non-stick frying pan over medium heat. Add the chicken and cook, turning occasionally, for 5 minutes or until brown all over. Transfer chicken to a 2L (8-cup) capacity ovenproof casserole dish.
Add onion and celery to the frying pan and cook, stirring, for 5 minutes or until soft. Add garlic and mushroom and cook, stirring, for 2 minutes or until mushroom is tender. Add tomato and stock cube and bring to the boil. Remove from heat. Add to casserole dish with the chicken.
Cover the casserole dish with a tight-fitting lid or foil. Bake in oven for 35 minutes or until chicken is tender. Add broad beans and half the thyme and cook for a further 10 minutes or until broad beans are tender. Remove from oven. Taste and season with pepper.
Meanwhile, cook the pasta in a large saucepan of boiling water following packet directions or until al dente. Drain well.
Spoon casserole into a large serving bowl. Sprinkle with remaining thyme and serve with pasta, if desired.