Add the coconut oil to a large frying pan or stovetop casserole pan and gently fry the finely chopped onions, celery, carrots and garlic for around 7 minutes on a low heat.
Add the mince and fry for another few minutes, breaking it up with a wooden spoon. Fry until browned (around 5-10 minutes).
Stir in the tomato puree, then pour in the beef stock. Allow to bubble on a medium heat for 5 minutes. Tip in the chopped tomatoes and sprinkle in the mixed herbs. Cover and simmer for an hour, stirring occasionally.
When the Bolognese sauce is almost ready, pre-heat the oven to 200C/180C fan/gas 6.
Take a teaspoon and scoop out some of the middle of each half of the zucchini/courgette. Chop the pulp finely and add it to the Bolognese sauce. Stir replace the lid and continue cooking the sauce.
Place the zucchini/courgette on a baking tray lined with baking paper, drizzle with avocado oil, season with salt and pepper and bake in the oven for 15 minutes.
Remove the zucchini/courgette boats from the oven and top each ‘boat’ with some of the Bolognese sauce. Sprinkle each boat with hazelnuts and return to the oven for a further 15 minutes. Serve straight away.