Slow Cooked Lamb Shanks Recipe

5-6 lamb shanks
1 red onion, sliced
8 or so garlic cloves, peeled
6 or so rosemary sprigs
2 tsp dried oregano
2 tsp fennel seeds
1 tsp turmeric
1 tsp smoked paprika
½-1 tsp chilli flakes (or chilli powder, or 2 fresh chillis, finely chopped)
Several grinds of black pepper
2 tbsp tomato paste
1 tbsp olive oil + a little extra
1 tbsp lemon juice
2 fennel bulbs, sliced vertically into wedges
350ml vegetable stock (preferably no added salt, I use this one) or water*
fresh mint, roughly chopped, to garnish