My stuffing consisted of the flesh and ingredients I happened to have in the house: olive oil, 1 red onion, 1 chopped clove of garlic, 75g rice, 60g diced Gruyere, a tbsp of cream cheese (I'm not sure that this was a good idea, but I thought the bit left in the tub needed using), salt, cayenne pepper. Extra or substitutional ingredients might have been pre-soaked raisins, toasted pine nuts, a few anchovies, and herbs such as flat-leaf parsley, tarragon, or thyme.
Cook the rice in the normal way. (There's plenty of advice, only some of it inconsistent, on this blog.) Meanwhile, finely chop the onion, and gently cook it with the garlic in a tbsp or two of olive oil. Chop up the courgette flesh, throw it into the pan, and gradually turn up the heat as it exudes water. Cook it on a high heat until the water evaporates. Stir in the rice, cheese, and seasoning.
Put the courgette halves in a baking dish or roasting tin, and stuff them with the mixture. Pour boiling water into the dish to a depth of between 50mm and 1cm. Bake at gas mark 6/200C for about 25 minutes, or until the courgette is soft and the stuffing is slightly browned on top.