Heat the oil in a pan and add the onions and garlic. Cook for 4-5 minutes over a medium heat, taking care not to brown.
Add the pork and beef mince and break up any clumps with a wooden spoon. Cook until there is no pink meat left.
Remove from heat and drain in a sieve, taking care that the holes are small enough so that only the excess liquid is drained off.
Place the meat into a bowl and season well with salt and pepper. Add the eggs, parsley and half of the cheese and mix well.
Pour a layer of the sauce over the bottom of an ovenproof dish.
Fill the tubes of cannelloni with the meat mixture and layer the tubes on top of the sauce. Continue until all the meat is used and then cover the tubes with the rest of the sauce. Top with the rest of the mozzarella cheese.
Cover with foil and place in a preheated 170 C / Gas 3 oven for 30 minutes. Remove the foil and cook for another 15 minutes.