To make the burgers: Place the mince, harissa paste, garlic, lemon juice, mint leaves, salt and pepper in a bowl and mix well to combine. With damp hands shape the mixture into 4 burgers.
To make the tzatziki: Mix together the yogurt, garlic, cucumber, lemon juice and chopped mint. Season to taste.
Heat the oil in a large frying pan over a medium heat and cook the burgers for 4–5 minutes on each side or until cooked to your liking. You can also cook the burgers on the barbecue.
Put some salad leaves on the bottom half of each roll, place a burger on top of the leaves. Spoon over some tzatziki and top with a little extra harissa paste. Serve with baby new potatoes or crispy potato wedges.