Make the vinaigrette: In a bowl, combine the red wine vinegar, lime juice, lemon juice, grapefruit juice, mustard, honey, salt and pepper. Whisk to combine. Slowly add the olive oil, whisking, until combined. Set aside.
To make the salad, shave 8 thin slices off the cucumber (preferably on a mandoline). Finely chop the avocado and red onion.
On each of 4 plates, use two cucumber slices to make a ring. Divide the smoked salmon evenly between the plates and place inside the rings. If you want, you can add a dash of the citrus vinaigrette to the salmon.
Top the smoked salmon with the avocado and red onions. Garnish with chopped cilantro and bean sprouts.