Heat the oil in a large frying pan over a medium heat. Add the onion and cook, stirring, for 6 to 8 minutes softening. Increase the heat, add the mince and cook, stirring, for 5 minutes until browned.
Add the Mediterranean seasoning and garlic to the pan and cook, stirring, for 1 minute. Add the tomatoes, half-fill the can with water, then add it to the pan with the oregano. Bring to the boil, then season and reduce the heat. Simmer for 20 minutes.
Heat the oven to 180C/160C fan/gas 4. For the topping - in a mixing bowl combine the yogurt, egg and half the feta. Season with pepper (feta is already salty).
Cook the macaroni in a large pan of boiling salted water according to packet instructions (until just al dente). Drain, then spoon half into a deep ovenproof dish and season with salt and freshly ground pepper. Top with the mince, then add the remaining macaroni, pressing down with the back of a spoon.
Spoon the yogurt topping over the pasta to cover, then scatter with the remaining feta to finish. Bake for 25 minutes or until golden and bubbling. Serve sprinkled with extra oregano, if you like.