Coarsely grate 1 onion and place in a large bowl with mince and Worcestershire sauce. Season and mix well to combine. Divide into 4 even patties slightly larger than your buns, using wet hands to shape the patties. Place on a tray, cover with plastic wrap and refrigerate for 30 minutes to rest.
Heat a large non-stick frying pan over medium-high heat. Thinly slice remaining onion and toss in a bowl with 2 tbsp oil. Season to taste. Cook onions, stirring occasionally for 8-10 minutes until golden brown. Set aside.
Meanwhile, heat a char-grill pan or barbecue over medium-high heat. Spray pineapple with oil and cook, turning occasionally for 3-4 minutes until browned. Set aside.
Brush burger patties with oil. Add burgers to char-grill pan, reduce heat to medium and cook, for 5-6 minutes each side, or until cooked through. Transfer to a plate to rest for 5 minutes.
To serve, top each bun base with lettuce, tomato, burger patty, pineapple, beetroot, chutney and onions. Sandwich with bun tops and serve with fries, if desired.
Use a light touch to form a loose patty; if you pack too densely the patty won’t cook.
Add 2 tbsp cold water to the beef mince for a lighter burger patty