Preheat the oven to 350°F.
Cut the tops off the sourdough loaves and scoop out the insides, leaving about a 1-inch thick shell. Reserve the bread you scoop out for later use.
In a large mixing bowl, combine the cream cheese, shrimp, crab meat, mozzarella cheese, mayonnaise, green onions, lemon juice, garlic powder, Old Bay seasoning, salt, and pepper. Mix until well combined.
Fill each hollowed bread loaf with the seafood mixture, packing it in tightly.
Place the filled bread bowls on a baking sheet and bake in the preheated oven for 25-30 minutes, or until the tops are golden and the filling is heated through.
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley before serving.
Serve warm with the reserved bread pieces for dipping.