This recipe creates four (4) serves. Visit the link below if you're want two (2) serves instead.
Thinly slice one onion and set aside. Finely chopped the remaining onion and place in large bowl with mince, mushrooms and herbs. Season with pepper. Mix with clean hands until well combined. Divide into four even portions. Shape portions into 1 cm-thick patties.
Heat oil in a large, deep non-stick frying pan over medium heat. Add sliced onion. Cook, stirring, until light golden. Transfer to a plate. Cover with foil to keep warm.
Add patties to same pan. Cook for 4-5 minutes on each side over medium-high heat, until evenly browned and cooked through.
Split rolls in half and toast lightly. Spread avocado over cut-sides of rolls. Top bases with lettuce, patties, tomato, beetroot, onion and chutney. Cover with roll tops to serve.