Put endive into a salad howl. Cut peel and pith from oranges and grapefruit. Holding each one over a bowl to catch juice, remove segments and halve. Arrange on top of endive.
Halve avocado, remove stone, slice or dice flesh, then add to salad.
To make the dressing, mix all the ingredients in a howl or screw-top jar with 2 tablespoons of juice. Spoon over salad, and serve.