Clam Toasts with Pancetta

Name: Clam Toasts with Pancetta
Ingredients: 4 tablespoons olive oil, divided, plus more for drizzling; 2 ounces pancetta (Italian bacon), finely chopped; 4 garlic cloves, 2 thinly sliced, 2 whole; ½ medium sweet onion, finely chopped; ½ small fennel bulb, finely chopped, plus ¼ cup fennel fronds; 2 wide 3-inch strips lemon zest; 1 bay leaf; ½ teaspoon ground fennel; 1 cup dry white wine, divided; 2 1½-inch-thick slices sourdough bread; 1 pound Manila or littleneck clams or cockles; ¼ cup parsley leaves with tender stems; Crushed red pepper flakes (for serving)