Mix together the oil, herbs, spices and garlic in a large sealable bag. Put the chicken breasts in the bag and mix thoroughly to cover. Bash the chicken with a rolling pin to flatten it a little, then set aside to marinate for at least 15 mins.
In a large bowl, mix all the ingredients for the bean salad. Stir well and set aside.
For the guacamole, scoop the flesh from the avocado and put it in a medium bowl, chopping it roughly with the side of the spoon. Add the rest of the ingredients and mix well. If you prefer your guacamole to be smoother, mash the avocado well with the olive oil and lime juice until it’s at your preferred consistency before stirring in the other ingredients.
Heat the grill. Line a grill pan with foil, place the chicken breasts on it and grill for 5 mins, checking occasionally. Once golden brown, turn and grill for a further 5-7 mins. Check the middle of the breasts after 5 mins and, if cooked through, remove from the heat.
Set aside 2 chicken breasts and 2 tbsp guacamole for Open rye sandwich (see 'goes well with', right). Place 1 warm chicken breast on each plate, with some bean salad and a dollop of guacamole on the side.