Avocado cream sauce: mash avocado using a fork, then mix in with the other ingredients.
Filling: mix vinegar, oil and coriander and season. Thinly slice apple, and immediately mix with sauce.
Spread avocado cream sauce on bottom half of bagel. Top with apples slices, lettuce leaves and Tilsit, season and sprinkle with nuts. Close with top half of bagel and serve.