Combine mince, onion, garlic, 1 tbsp oil, sauce, and oregano in a bowl. Mix together using clean hands. Divide into four portions and shape into patties 11cm in diameter. Make a dent in the centre with your thumb (this helps to prevent them from shrinking during cooking). Stack patties, separating them with baking paper, and chill for 15 minutes.
Heat a frying pan or barbecue on medium-high heat. Brush sides of patties with oil and cook for 5 minutes each side or until cooked through.
Fill rolls with lettuce, tomato, cucumber, and onion. Top with a patty, extra cucumber or onion, if desired, and serve with chipotle chilli mayo.
Chipotle Chilli Mayonnaise
To make mayonnaise, whisk all ingredients together in a large bowl until smooth. Cover and refrigerate until ready to serve.