Place a 3-inch ring mold on a plate. Layer 2 to 3 pieces of salmon in the mold. Sprinkle salt and pepper over salmon. Sprinkle a little Champagne vinaigrette over the salmon and top with croutons. Peel and slice the avocados into 1/4-inch cubes. Squeeze lemon juice over avocado to avoid discoloration; this will also compliment the flavors of the dish. Add a little wasabi to the avocados and gently toss. Place 3 to 4 slices of the avocado on top of the salmon. Repeat the layers 1 more time. Remove the ring mold and garnish the top with a small piece of chive. Repeat to make a total of 4 tiers.