Mix the mayonnaise, chives, lemon juice, salt and pepper together.
Thinly butter the rye bread and cut each slice in half.
Peel and slice the avocado. Baste the slices with lemon juice so that they don't discolour so fast.
Arrange 2 or 3 slices of avocado on each half of bread and arrange a slice of smoked salmon on top. Spoon the mayonnaise mix over the top. Garnish with a thinly sliced half slice of lemon if desired.