Mix together the guacamole ingredients (avocado-coriander). Season and set aside for the moment.
For the burgers, heat the oil in a pan and saute the onion and the remaining two garlic cloves for a few minutes. Allow them to cool, then tip into a bowl and add the parsley, mince and chilli powder. Season and mould into four burgers.
Brush the burgers with oil and grill for about 4 minutes each side until cooked through. Cook the pepper and onion slices on the barbecue, until softened.
Serve in toasted buns with lettuce, the peppers and onions, and some guacamole.