Place the sweet potato in a saucepan of cold salted water and bring to the boil.
Turn the heat down to a slow simmer and cook the potatoes for ten minutes.
Meanwhile, gently fry onion and garlic in the oil for 3-5 minutes until softened.
Add the Brussels sprouts and stir fry for a further three minutes or until they are softened.
When the potatoes are cooked, strain them and place back in the pan. With a potato masher, mash the potatoes until they are lump-free. Add the butter and the salt and freshly ground black pepper and stir through.
Add the onion and sprouts. Mix well. Set aside and keep warm while you cook the meat.
Heat a griddle pan until smoking. With a pastry brush, brush the mustard and honey onto the gammon steaks.
Griddle them for 2-3 minutes on each side.
Finish them in the oven for a further three minutes.
Serve the bubble and squeak on a plate and top with the glazed gammon.