Add the onion, ketchup, and oyster sauce to a food processor and pulse until you have a rough paste. Transfer the sausage meat to a large mixing bowl. Add the onion paste, egg yolk, 60ml (¼ cup) water, and chopped parsley. Mix with your hands until just combined — do not overwork. Divide the mixture into 8 equal portions (about 125g / 4.5 oz each). Roll each into a ball, then flatten into a patty roughly 1cm (½ inch) thick and slightly wider than your ciabatta buns (patties shrink as they cook).

Heat a large non-stick or cast-iron skillet over medium-high heat — do not add oil; the sausage meat will render its own fat. Place the patties in the pan (work in batches if needed) and cook for 3–4 minutes on the first side until deeply golden. Reduce the heat to medium-low, flip, and cook for a further 5–6 minutes until the internal temperature reaches 160°F / 71°C on an instant-read thermometer. Remove to a plate and rest briefly.

While the burgers cook, fry the bacon rashers in a separate skillet over medium heat until crispy, about 3–4 minutes per side. In the remaining bacon fat, fry the eggs to your preference (sunny-side up works best here). Meanwhile, split the ciabatta buns and toast the cut sides under the grill or in a dry pan until lightly golden.

Place the cooked patties on a baking sheet and top each with a slice of cheese. Slide under a hot grill (broiler) set to high, about 260°C / 500°F, for 1–2 minutes until the cheese is melted and bubbling. Set each patty on the bottom half of a toasted ciabatta bun, add a tomato slice, a rasher of bacon, and a fried egg. Crown with the top bun and serve immediately.