Baked cod with crab and herb crust

Name: Baked cod with crab and herb crust
Ingredients: * olive oil, to coat the pan; * 2 6-oz cod fillet, the thicker the better; * 1 cup claw crab meat, picked over for shell; * 1 cup fresh breadcrumb; * finely grated zest of 1 lemon; * 1/3 stick unsalted butter, melted; * 3 tbsp chopped fresh basil; * 1 tbsp finely chopped chive; * 1 tsp finely chopped parsley; for the sauce; * 1/4 cup creme fraiche; * 1 tbsp mayonnaise; * 1/2 cup watercress leave, finely chopped; * 1/2 shallt, minced; * 1 tsp dijon mustard; * 2 tsp caper, rinsed and chopped; * 1 tsp lemon juice, or more to taste