Steaming Fresh Clams: Add the clams to a large pot with 1/2 cup water and a splash of white wine or lemon juice. Cover and steam over medium heat for 7-8 minutes, or until the clams open. Reserve the cooking liquid and discard any unopened clams.Carefully remove the cooked clam meat from the shells, then dice the meat into bite sized pieces. Break the shells in two and choose about 14-16 to use for filling. Wash the shells under hot, soapy water and pat them dry. Using Canned Clams: Open the cans and drain about half of the liquid. Dice any large clams into bite sized pieces.
Mince the garlic, parsley, and oregano. Measure and mix together the clams, 3 tablespoons of reserved liquid, oil, garlic, herbs, seasonings, breadcrumbs, and parmesan cheese. The mixture should be fully moist- not dry and crumbly but also not watery. If needed, mix in a bit more reserved clam liquid, 1-2 teaspoons at a time.
Spoon the mixture to fill each clam shell, pressing it gently into the shell. Set the filled shells on a baking sheet. Bake in the oven for 25-30 minutes, or until heated through and crispy on top.
Allow the baked clams to cool slightly, then carefully transfer them to a plate. Sprinkle with lemon juice and serve.
To make in advance: Cover the prepared, uncooked clams with plastic wrap or set in an airtight container and refrigerate up to 24 hours. Remove from the refrigerator, set the clams on a baking sheet, and cook according to the recipe.To freeze: Lay the prepared, uncooked clams on a baking sheet and freeze for 1-2 hours. Transfer the partially frozen clams to an airtight bag and squeeze as much air out as possible before closing the bag. Return to the freezer. Defrost in the refrigerator overnight and cook according to the recipe. Use within 2 months for best taste.