Take a mixing bowl and add the ingredients as you prepare them.
Cut the avocado in half lengthwise. Remove the pit, peel off the skin, and dice the flesh into small cubes. Place them in the bowl and drizzle with a bit of lemon juice to prevent browning.
If you're using a fresh mango, peel it, remove the flesh by cutting around the pit, and dice it into small cubes as well.
Peel the shrimp (remove head and shell) and cut them into pieces similar in size to the avocado and mango cubes.
Add the mango vinegar, then gently mix in the chopped dill, pepper, and salt.
For plating, use round molds or a small ramekin: fill them with the tartare, press down gently with a spoon, then unmold before serving.