Make the herby cream cheese. Combine the cream cheese with the minced chives, dill, lemon zest, 1 tbsp of lemon juice, and a pinch of salt and pepper. Taste and, if needed, add more salt and pepper.
Mash the avocado and season. Mash the avocado and add a pinch of salt, ground black pepper, and a squeeze of lemon juice (about 1 tbsp). Taste and if needed, add more salt and pepper.
Slice the croissants. Use a serrated knife to slice the croissants.
Assemble and serve. Add herb cream cheese on the bottom half of the croissant, smoked salmon on top of the cream cheese, and mashed avocado on the top half of the croissant. Bring the halves together to make the croissant sandwich and serve.
