Heat your oven to 200°C/Fan 180°C/ Gas 6. Fill the kettle and boil then pour 200ml hot water into a jug. Crumble in the stock cube and stir well to mix.
Scrub the potatoes and cut into bite sized halves or quarters. Halve the fennel. Cut each half into four. Halve the lemon lengthways. Remove any pips. Cut one half into thin slices. Juice the remaining half. Peel the garlic but leave the cloves whole.
Heat 1 tbsp olive oil in a heavy-based casserole dish or frying pan. Add the chicken, skin side down. Cook for 4-5 mins till the skin is crispy and golden.
Turn the chicken so it's skin side up. Add 2 tsp of the fennel seeds. Sizzle for 1 min then add the potatoes, fennel, lemon slices, garlic and rosemary. Season. Stir to tumble together.
Pour the stock into the casserole dish. Place in the oven, uncovered, and cook for 35-40 mins till the chicken is cooked through and the potatoes are roasted. If you're using a frying pan, transfer everything to an ovenproof dish or roasting tin.
While the chicken is cooking, fill a pan with the hot water from the kettle. Slice the spring greens. Pop them in a steaming basket or colander over the pan. Steam the greens for 5 mins. Drain. Squeeze the remaining lemon juice over the greens.
Using a fork, squash the garlic cloves from the casserole in the cooking juices. Stir well. Serve with the lemony greens.