mix whole greek yogurt with mustard powder and fresh tarragon leaves, drizzle tablespoon of olive oil while mixing with fork or small blender to emulsify.
slice fresh avocado.
slice red onion.
slice large beef steak tomato into thick slice.
drizzle juice of lemon over avocado, onion and tomato.
sprinkle finely chopped basil and fresh cracked pepper over slices.
lightly toast pumpernickel bread.
spread yogurt mixture over both slices of bread.
layer avocado, onion and tomato.
shave parmigiano-reggiano over.
add layer of arugula/watercress.
close sandwich and sprinkle coarsely cut basil over bread.