Thinly slice the onion into rounds, then separate into rings. Crush or finely chop 2 garlic cloves. Coarsely grate the cheese. Put the beef mince and garlic in a large bowl and season with salt and pepper. Using damp hands (see Kitchen hack), combine well, then shape into 2 equal patties, slightly larger than the base of a bread roll.
Step 2 — Cook onion rings
Put 1 tbs plain flour in a bowl and season with salt and pepper. Dust the onion in the seasoned flour. Heat a generous drizzle of olive oil in a medium frypan over medium-high heat. Cook the onion rings, stirring occasionally, for 6-7 mins until crisp and golden. Remove from the pan and drain on paper towel.
Step 3 — Pan-fry patties
While the onion is cooking, preheat the grill to high. Line an oven tray with foil. Heat a drizzle of olive oil in a separate medium frypan over medium-high heat. Cook the patties for 3-4 mins each side until cooked through. Remove the pan from the heat.
Step 4 — Toast rolls
Meanwhile, cut the bread rolls in half. Put on the lined tray, cut-side up, and scatter the cheese over the roll bases. Grill for 1-2 mins until lightly toasted and the cheese is melted. Combine 1 tsp olive oil and 1 tsp red wine vinegar in a large bowl and season with salt and pepper. Add the salad leaves and toss to coat.
Step 5 — Serve up
Layer the cheesy roll bases with some salad leaves, the beef patties and onion. Dollop with the burger sauce, then sandwich with the roll tops. Serve with the remaining salad leaves and enjoy!
Step 6 — Kitchen hack
If you handle the beef mince with dry hands, you'll find the mince will stick to them. Rinse your hands under water or lightly oil them before combining and shaping the patties.