In a heavy based pot on medium heat, saute onion, garlic, celery, carrot and fennel with a few good glugs of olive oil and a couple of pinches of salt. This will take a few minutes. It will become fragrant and everything will soften.
Add the zucchini and parsley and sautee for another couple of minutes
Add the diced lamb shoulder, stirring occasionally so the outside of the meat becomes golden. After a few minutes add the tomato paste. The tomato paste will begin to caramelise on the bottom of the pan and then it's time to add the tomatoes followed by the stock.
Give it a good stir, pop the lid on and turn the heat down to low and let the sauce do its thing. It's good to check the sauce every now and then and give it a stir
After roughly 2.5 hours, the meat should be soft and tender, and the sauce will have reduced and thickened
Cook pasta and serve together with the ragu