Cut the avocado in half lengthwise and remove the pit.
Scoop out the flesh with a spoon, place in a blender, add the juice of half a lemon and puree. Pour the juice of a whole lemon into a small baking dish and place the two avocado halves in with the cut side down.
In a blender, puree the coarsely divided trout pieces with the avocado flesh. Pour the contents of the blender into a bowl, mix well with sour cream, the plucked dill needles and the spices and season to taste.
Cut a piece off the rounded outer skin of each avocado half to give them a secure stand.
Fill the avocado halves with the mousse.
Toast the toast. Arrange each avocado half on a plate, garnish each with 2 sprigs of dill and other decorations of choice, and serve with the toast.
