In a large bowl, mix all the burger ingredients together. Season. Using slightly damp hands, shape the mixture into four 5cm burgers. Cover and chill for 20 minutes.
Meanwhile, prepare the pea and tomato relish: in a small bowl, mix all the ingredients together, season to taste and set aside.
Cook the burgers under a preheated moderate grill or on a prepared BBQ for 6–8 minutes on each side until thoroughly cooked and meat juices run clear.
Serve in burger buns with salad leaves, a spoonful of the relish and selection of accompaniments of your choice.