Mix ham, parsley, garlic, half the pancetta, the ground beef, the parmesan and the egg into a bowl with salt and pepper to taste. With a little sharp knife (or use a spoon) cut out the meat from the courgette but make sure to leave the shells intact. Fill them with your meatmixture.
Heat the butter and oliveoil in a wide pan (it will have to fit the courgettes too!), add the onion and the rest of the pancetta and bake for about 5 minutes on low; stir occasionally. Add the courgette and bake them also for a few minutes.
Mix the passata with 175 ml of warm water and put the mixture in the pan. Add salt, cover and let it simmer for about 20-30 minutes or until the meat is cooked and the courgettes are tender.
Put them in a hot bowl and pour a little of the cooking sauce over the top.