For the sandwich, place the steak onto a plate and season with salt and freshly ground black pepper. Rub in the garlic, drizzle with the oil and set aside to marinate.
For the chutney,heat the oil in a saucepan over a medium-high heat. Add the onion, red pepper and garlic and cook for five minutes, to soften.
Add the brown sugar to the saucepan and cook for a further ten minutes.
Add the butter and vinegar to the saucepan and cover, allowing to cook gently for a further five to ten minutes.
Meanwhile, make the mustard sauce by mixing together all of the sauce ingredients and seasoning to taste with salt and freshly ground black pepper.
To cook the steak, heat a griddle pan until smoking. Add the steak an cook for two minutes on each side, or to taste and remove from the heat.
To serve, spread the ciabatta with a thick layer of mustard sauce, top with the steak and then spoon over the chutney.