Preheat the oven to 200C/400F/Gas 6.
For the beef, place the breadcrumbs and the herbs into a bowl and mix together.
Add the mozzarella to coat with the herbs and breadcrumbs and set aside.
Heat an ovenproof griddle pan until smoking. Rub the beef with the olive oil and season with salt and freshly ground black pepper. Place the beef onto the griddle and cook for two minutes on each side, to brown the meat.
Place the mozzarella with herby breadcrumbs onto the beef. Transfer to the oven to roast for five minutes, or until the beef is cooked to your taste, then rest on a warm plate for one minute.
To make the sautéed potato, heat the oil and butter in a frying pan. Add the rosemary and garlic and fry for one minute.
Add the potatoes and fry over a medium heat, turning the potatoes regularly, until golden.
To make the onion rings, heat the oil in a deep, heavy bottomed saucepan until a breadcrumb sizzles in it the oil. (CAUTION: hot oil can be dangerous - do not leave unattended!)
Place the flour, baking powder, egg and spring water into a large bowl and whisk together to make a batter.
Dip the onion rings in the batter and then carefully place into the hot oil and deep-fry for 2-3 minutes, until cooked and golden. Carefully remove with a slotted spoon and drain on kitchen towels and sprinkle with salt.
To make the roasted tomato, place the tomatoes on a small baking sheet, drizzle with oil and season, to taste, with salt and freshly ground black pepper. Place into the oven and roast for ten minutes until cooked and soft.
To make the mushroom sauce, heat the butter and oil in a medium frying pan over a medium heat. Add the garlic and onion and fry for 4-5 minutes, until softened.
Add the mushrooms and mustard and fry for two minutes.
Add the cream, bring to the boil, reduce the heat and simmer for five minutes, until the sauce has thickened. Season, to taste, with salt and freshly ground black pepper.
To serve, place the cheese covered beef in the centre of a warm plate and serve the sautéed potatoes, onion rings and roasted tomatoes in piles beside. Pour over the mushroom sauce.