Cover clams in cold water, allowing them to soak for 15 minutes then use a food brush to remove any dirt or sand from the outside of the shell.
Transfer the cleaned clams to a pot large enough to hold the clams in a single layer. Add enough water to just cover the bottom of the pot, cover & bring to boil and simmer for one minute. Discard any that do not open.
Pour off and reserve the clam liquor from the bottom of the pot.
Remove the clam meat from the shells. Reserve the shells and coarse chop the clam meat.
Saute the garlic, onion and celery in the olive oil in a shallow pan until the onion turns translucent.
Add the chopped clams, lemon juice, oregano, parsley, salt, pepper and about one cup of the reserved clam liquor to the sauteed vegetables and bring to boil then remove from heat.
Add bread crumbs and mix well. Consistency should resemble that of oatmeal. Add additional clam liquor or bread crumbs to get correct consistency.
Break apart reserved clam shell by twisting and fill each half shell with the clam mixture.
Place filled shells on a baking sheet and bake in a 400 degree oven for about 15 minutes of until internal temperature reaches 160 degrees.