Purée parsley with bread crumbs and 1/4 cup oil in a food processor.
Cook onion, garlic, and red pepper flakes in remaining 2 tablespoons oil in a medium skillet over medium heat, stirring, until pale golden, about 5 minutes. Add wine and clam juice and boil, stirring, until slightly reduced, 1 to 2 minutes. Stir in clams and cook until heated through, then stir in parsley purée. Remove from heat and season with lemon juice and salt.