Combine mince, oats and 2 tablespoons chutney in a bowl. Season with salt and pepper. Shape mixture into two 1.5cm-thick patties. Place on a plate. Cover with plastic wrap. Refrigerate for 20 minutes if time permits.
Make caramelised onion Heat oil in a non-stick frying pan over medium heat. Cook onion, covered, stirring, for 8 to 10 minutes or until softened. Add sugar. Cook, stirring occasionally, for 4 to 5 minutes or until golden and caramelised.
Spray a barbecue plate or chargrill with oil. Heat on medium-high heat. Cook patties for 5 minutes each side or until cooked through. Place on a plate. Cover to keep warm. Spray mushrooms with oil. Season with salt and pepper. Add mushrooms. Cook for 4 minutes each side or until tender. Place rolls, cut side down, on barbecue. Cook for 1 to 2 minutes or until lightly toasted.
Place one-quarter of the lettuce, beetroot and tomato on roll bases. Top 2 bases with beef patties and half the onion mixture. Top remaining bases with mushrooms, remaining onion mixture and remaining chutney. Sandwich with roll tops.
Recipe courtesy of taste.com.au
Serving size 4