Slice the avocados in half lengthwise, remove the pit and peel them.  Chop the avocado into large dice, about 1/2-inch.  Add the avocado to a small bowl with the vinaigrette, toss and refrigerate for 2 hours. 

Add the crab, crawfish and parsley to the avocado. Fold the mixture taking care not to break the lumps of crabmeat or to mash the soft avocado.  Chill the mixture for 1 hour before serving.

Add the lettuce to a large mixing bowl with the olive oil, salt and pepper. Toss the mixture until the leaves are evenly coated. Slice the hearts of palm on a bias, end to end, creating long triangular shapes.

Create a bed of lettuce on 6 chilled plates. Evenly distribute the marinated avocado, crawfish and crab salad atop the lettuce.  Lean 2 slices of hearts of palm against the avocado salad for added flavor and garnish.