Clean the mackerel from the skin and bones. In a bowl place the fish, cream cheese, chopped dill and mustard. Chop immersion blender until smooth. Try the pate. If you need salt, I salted. Add the lemon juice, I also didn't do because I didn't want the acidity in the paste. Pepper.

Peel the cucumber, finely chop and mix with the pate.

Serve on slices of black bread, and for festive use the ADF of the puff pastry.