Scoop out and discard courgette seeds, leaving the hollowed-out shells. Sprinkle the garlic salt into the hollowed-out courgette and set aside.
Heat olive oil in a frying pan over medium heat and cook the onion and garlic until the onion is translucent, about 5 minutes. Remove from heat and allow to cool.
In a mixing bowl, mix the minced beef, eggs, breadcrumbs, basil, carrot and Parmesan cheese together with the onion mixture.
Stuff the courgette halves with the meat mixture and place them into a baking dish. Spoon about half the pasta sauce over the courgette, covering all the meat and allowing sauce to drip down the sides of the courgette shells.
Bake in preheated oven until the meat is no longer pink in the centre and the courgette halves are tender, about 45 minutes. An instant-read thermometer inserted into the centre should read at least 70 degrees C.
Sprinkle mozzarella over the courgette and return to oven until the cheese melts, about 5 more minutes.
Heat the remaining pasta sauce in a small saucepan over medium heat while the courgette halves are cooking. Serve the courgette with the additional sauce on the side.