Crab Salad with Avocado and Pomelo

Name: Crab Salad with Avocado and Pomelo
Ingredients: DRESSING:; 2 tbsp freshly squeezed orange juice; 1 1/2 tbsp extra virgin olive oil; 2 tbsp white wine vinegar; 2 tsp finely chopped fresh tarragon or chervil; 1/2 tsp freshly grated orange zest; 1/2 tsp salt; 1/4 tsp dry mustard; 1/4 tsp freshly ground black pepper; SALAD:; 2 heads butterhead lettuce, separated into leaves (about 8 c); 2 med sweet onions, sliced (about 2 c); 2 pomelos, peeled and cut into sections (about 4 c); 1 med avocado, peeled, pitted, and sliced; 1 C lump crabmeat (available at fish counter); 1 tbsp chopped toasted skinless hazelnuts