Place the quinoa in a large pan and cover with water. Bring to the boil and cook for 20 minutes, until tender. Drain well and set aside.
Meanwhile, heat the butter in a large frying pan, add the garlic and prawns and cook for 3 minutes, until the prawns are cooked through.
Place the prawns in a large bowl and stir in the tomatoes, dill, parsley, onions, avocado, chopped olives, extra-virgin olive oil and the lemon juice. Stir in the drained quinoa and season well to taste.
