Mix herb salt ingredients together in a small bowl and set aside.
In a separate small bowl mash avocado with lemon juice, lemon zest and a pinch of salt until smooth and creamy.
Using a sharp knife slice English cucumbers into ½ inch rounds on a cutting board. Pat each cucumber slice dry with paper towels. Lay out in a single layer on your board or platter.
Spoon avocado mash onto each round. Top with cold-smoked salmon, a generous sprinkle of herb salt and fresh dill or fresh chives.