Step 1
Spray a non-stick frying pan with oil and heat over medium-high heat. Cook patties, turning, for 10-15 minutes or until cooked through. Top with cheese and cook for 1 minute or until the cheese just melts.
Step 2
Meanwhile, for onion rings, combine the flour, polenta, chilli powder and salt in a large bowl. Season with freshly ground black pepper. Make a well in centre. Add buttermilk and whisk until well combined.
Step 3
Add enough oil to a saucepan to come halfway up side. Heat over medium-high heat until oil reaches 180C on a cook’s thermometer. Dip one-third of the onion rings, 1 at a time, into the buttermilk batter to evenly coat, then add to the hot oil. Deep-fry for 2-3 minutes or until crisp and golden. Drain on a plate lined with paper towel. Repeat with remaining onion rings and buttermilk batter.
Step 4
Spread the base and tops of the rolls with mayonnaise. Top bases with lettuce, tomato, gherkin, meat patties and onion rings. Top with roll tops.