Mix the rice and vegetable stock in a pot and bring to the boil. Reduce heat to low, cover and simmer 45 minutes or until rice is tender.
Preheat oven to 180 C / Gas 4. Lightly grease a large casserole dish.
Heat the olive oil in a frying pan over medium heat and cook the onion until tender. Mix in the courgette, chicken and mushrooms. Season with cumin, salt and ground cayenne pepper. Cook and stir until courgette is lightly browned and chicken is heated through.
In large bowl, mix the cooked rice, onion, courgette, chicken, mushrooms, beans, chillies, carrots and 1/2 the Gruyere cheese. Transfer to the prepared casserole dish and sprinkle with remaining Gruyere.
Cover casserole loosely with foil and bake 30 minutes in the preheated oven. Uncover and continue baking 10 minutes or until bubbly and lightly browned.
Diced green chillies can be purchased online. Alternatively, you can use fresh chillies to taste.