Heat the oven to 200°C/Fan 180°C/Gas 6. Rinse and trim the fennel. Save any frondy bits for garnishing. Slice the fennel into 8 wedges. Place on a baking tray. Drizzle with olive oil. Season. Pop the fennel in the oven. Roast for 10 mins.
Peel and crush or grate the garlic. Drain and rinse the beans. Peel the potatoes. Roughly chop them. Fill the kettle and boil it.
Warm a dry frying pan over a low heat. Toast 1 tsp each of the coriander and cumin seeds till they smell aromatic and nutty. Roughly crush them using a pestle and mortar or the end of a rolling pin. Rub the spices in to the lamb steaks. Season.
Warm a glug of olive oil in a pan. Fry the garlic for 30 seconds. Add the beans and potatoes. Crumble the stock cube into the pan. Pour in enough hot water from the kettle to cover the veg. Cover. Simmer for 15-20 mins till the potatoes are soft.
Warm a glug of olive oil in the frying pan. Add the spiced lamb steaks. Cook for about 2 mins each side to brown them.
Add the lamb and the tomatoes to the baking tray. Roast for 10 mins till the tomatoes are soft and the fennel is caramelised and tender. Take the lamb and veg out of the oven. Cover with foil. leave to rest for 5-10 mins.
While the lamb rests, drain the beans and potatoes, keeping the water (drain them over a bowl). Tip back into the pan. Mash them with a splash of the cooking water. If they seem dry, add a splash more water till you get the consistency you want.
Taste the mash and adjust the seasoning. Serve with the lamb and roast veg. Sprinkle with any fennel fronds you saved in step 1.