Pre heat oven to 150c / 300 f (fan forced)
In a large flameproof casserole dish or dutch oven, fry lamb shanks over medium-high heat, for about 12 - 15 mins or until browned on all sides, and remove to a plate (you may need to do this in batches - see notes).
Using kitchen towel/paper, carefully wipe out any excess oil from the pan.
Add bacon, carrot, fennel and onion to the pan, cook stirring over medium-high heat for 5 - 8 mins or until veg starts to soften.
Add garlic and tomato paste, and cook stirring for 1 min.
Add wine and allow to simmer for 2 -3 mins, or until wine starts to reduce.
Add thyme, ground fennel seeds and bay leaf to pot.
Add back shanks and any resting juices, nestling the shanks into the veg as best you can (see note), top with stock and bring to a simmer.
Bake, covered for 3 hours.
At this stage lamb should be tender. Turn up oven temperature to 180 c / 350 f, add couscous to liquid making sure it is all submerged and bake uncovered for 35 mins or until couscous is cooked through.