Flake the smoked mackerel fillet away from the skin and divide into large chunks; remove any remaining bones. Cut the cucumber into thin strips or half-moons and the avocado into slices.
Distribute the salad leaves over a plate and arrange the cucumber and avocado between them. Top with the mackerel pieces so they're nicely distributed.
Mix the olive oil with the lemon juice, salt and pepper into a fresh dressing and drizzle over the plate. Chop the dill finely and sprinkle it over the salad last. The combination of fatty fish and avocado provides plenty of healthy fats and keeps you satisfied for a long time.