Heat your oven to 180°C/Fan 160°C/Gas 4. Break the cauliflower into small florets. Chuck them in a pan and cover with boiling water. Simmer for 15-20 mins till the cauliflower is very tender.
While the cauliflower cooks, warm 1 tsp oil in a pan. Chop the chicken into bite size chunks and add to the pan. Fry for 5 mins till they’re golden brown all over. Turn now and then.
While the chicken cooks, trim and finely slice the leek into rings. Roughly chop any large mushrooms. Trim the rough ends from the fennel and finely slice the rest. Peel and crush the garlic.
Add the leek, fennel and all the mushrooms to the chicken. Chuck in the bay leaf and season well. Cook over a medium heat for 5 mins till the veg are soft and any excess water has cooked off. Stir often.
Stir the garlic into the pan. Crumble in the stock cube. Pour in 100 ml boiling water. Taste and adjust the seasoning if it needs it.
Drain the cauliflower and return to the pan. Mash, then stir over a low heat for 2-3 mins to cook off any excess water. Stir in the yogurt and season well. Finely chop the parsley leaves. Add most of them to the mash.
Ladle the pie filling into a 1 ltr ovenproof dish. Top with the cauliflower mash. Bake for 30 mins till the pie is golden brown and bubbling.
Serve the pie in warm, shallow bowls or plates, scattered with the remaining parsley.