Steam clams in a covered skillet filled with a small amount of water. Discard any clams that do not open. Remove top shell and discard. Leave the clam on the remaining half-shell, but loosen the meat by slicing it at the point where it is attached to the shell. Place on a baking sheet and set aside.
Fry bacon until crisp and set aside on paper toweling to drain. Pour off most of the bacon drippings except for about 1 tablespoon (enough to coat the bottom of the pan). Saute scallions, parsley and thyme in the bacon drippings for a couple of minutes to integrate flavors. Remove from heat and stir in bread crumbs. Crumble in bacon and combine. Season with salt and pepper as needed.
Preheat the broiler. Spoon herb mixture over the clams on the half shell and sprinkle a small amount of Parmesan on top of each. Toast in the broiler and serve garnished with parsley sprigs.