For the burger, place the beef, garlic, breadcrumbs and egg into a small food processor, season well with salt and freshly ground black pepper and blend until well combined.
Remove the mixture from the food processor and shape into a large pattie, using your hands.
Heat a griddle pan and brush it with oil. Place the burger into the pan and cook for 4-5 minutes on each side, or until cooked to your liking. Remove the burger from the pan and set aside in a warm place.
In the same pan, fry the goats' cheese for 1-2 minutes on each side, or until golden-brown.
For the onion rings, place the vegetable oil into a deep, heavy-bottomed saucepan and heat until a small cube of bread sizzles and turns golden when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Place the cornflour, plain flour and sparkling water into a bowl and whisk together to make a light batter. Dip the onion rings into this mixture to coat.
Carefully place the onion rings into the hot oil and deep fry for 3-4 minutes, or until golden-brown and crisp. Remove from the oil using a slotted spoon and drain on kitchen paper.
To serve, place the burger onto a slice of toasted ciabatta and top with the rocket and goats' cheese and the remaining slice of ciabatta, with the onion rings alongside.